Magnetoresistance effect element, magnetic head, magnetic head assembly, magnetic storage system

ABSTRACT

Disclosed are a high-sensitivity and high-reliability magnetoresistance effect device (MR device) in which bias point designing is easy, and also a magnetic head, a magnetic head assembly and a magnetic recording/reproducing system incorporating the MR device. In the MR device incorporating a spin valve film, the magnetization direction of the free layer is at a certain angle to the magnetization direction of a second ferromagnetic layer therein when the applied magnetic field is zero. In this, the pinned magnetic layer comprises a pair of ferromagnetic films as antiferromagnetically coupled to each other via a coupling film existing therebetween. The device is provided with a means of keeping the magnetization direction of either one of the pair of ferromagnetic films constituting the pinned magnetic layer, and with a nonmagnetic high-conductivity layer as disposed adjacent to a first ferromagnetic layer on the side opposite to the side on which the first ferromagnetic layer is contacted with a nonmagnetic spacer layer. With that constitution, the device has extremely high sensitivity, and the bias point in the device is well controlled.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a divisional application of Ser. No. 09/973,235filed Oct. 10, 2001, which is a continuation of application Ser. No.09/332,440, filed on Jun. 14, 1999 now U.S. Pat. No. 6,338,899, andclaims priority to the Japanese Application nos. 10-185475, filed onJun. 30, 1998, 10-237821, filed on Aug. 24, 1998, 11-097072, filed onApr. 2, 1999 the entire contents of which being incorporated herein byreference.

FIELD OF THE INVENTION

The present invention relates to a magnetoresistance effect device, amagnetic head, a magnetic head assembly, and a magneticrecording/reproducing system. More precisely, it relates to amagnetoresistance effect device, a magnetic head, a magnetic headassembly, and a magnetic recording/reproducing system, in which is useda giant magnetoresistance effect element having high sensitivity andhigh reliability.

BACKGROUND OF THE INVENTION

The recent tendency in the art is toward small-sized, large-capacitymagnetic recording media, for which there are increasing greatexpectations of high-power MR heads (magnetoresistance effect heads).For the MR film which is the basic constituent element in those MRheads, widely noticed is a spin valve film having a multi-layeredmagnetic film with a sandwich structure of magnetic layer/nonmagneticlayer/magnetic layer, in which one magnetic layer is pinned for itsmagnetization owing to the magnetic coupling bias applied thereto (thislayer may be referred to as a “pinned magnetic layer” or “pinned layer”)while the other magnetic layer is reversed for its magnetization owingto the applied magnetic field (this layer may be referred to as a “freemagnetic layer” or “free layer”). The spin valve film of that typeproduces a giant magnetoresistance effect (GMR) through the relativeangle change in the magnetization direction between those two magneticlayers.

As other types of MR films, known are an anisotropic magnetoresistanceeffect film (AMR film) made of an NiFe alloy or the like, an artificiallattice film, etc. Though smaller than that in an artificial latticefilm, the MR ratio in a spin valve film is at least 4% and is muchlarger than that in an AMR film. A spin valve film can saturate itsmagnetization even in a low magnetic field, and is therefore suitable toMR heads. MR heads incorporating such a spin valve film receive muchexpectations for their practical applications. Specifically, forincreasing the recording density in magnetic recording on magnetic discsand the like, high-sensitivity GMR heads (giant magnetoresistance effectheads) are indispensable.

Early GMR heads incorporate, in its GMR device, a spin valve film thatcomprises a free layer, a nonmagnetic spacer layer, a pinned magneticlayer and an antiferromagnetic layer. In those, the increase in thesensitivity of the film is indispensable for increasing the recordingdensity through reduction in the recording track width. However, if thefree layer is thinned so as to increase the sensitivity of the film forthat purpose, the stray magnetic field from the pinned magnetic layerwill shift the bias point. In that case, it is often difficult toeffectively correct the thus-shifted operating point by the currentmagnetic field.

On the other hand, a so-called laminated pinned ferromagnetic layer(hereinafter referred to as “SyAF”, or “Synthetic AF”) has been proposed(U.S. Pat. No. 5,465,185), which comprises two ferromagnetic layers asantiferromagnetically coupled via an antiferromagnetically couplinglayer existing therebetween. In principle, theantiferromagnetically-coupled, pinned layer of that type would producevery small stray magnetic field, thereby readily ensuring the operatingpoint.

One case of a spin valve film with SyAF is referred to, in which one ofthe two ferromagnetic layers adjacent to the nonmagnetic spacer layer isa ferromagnetic layer A while the other adjacent to theantiferromagnetic layer is a ferromagnetic layer B and in which theferromagnetic layer A and the ferromagnetic layer B have the samemagnetic thickness, thickness × saturation magnetization. In that case,the stray magnetic fields from the layer A and layer B cancel each otherso that there is substantially no stray magnetic field generated by thepinned layer. As a result, the pinned layer of that type is no moresusceptible to a magnetic field and has the significant advantage ofstable pinned magnetization at around the blocking temperature, Tb, atwhich the magnetic coupling bias of the antiferromagnetic layer is lost.

SUMMARY OF THE INVENTION

The problem with the present technology, that an object of the presentinvention is to resolve, is that the inventors found, the bias pointdesigning in an applied sense current is difficult, especially in deviceusing thin free layer so as to increase the sensitivity of output signalfor high density recording.

In a first aspect, the present invention provide a magnetoresistanceeffect element that attains the object mentioned above comprising anonmagnetic spacer layer, a first ferromagnetic layer and a secondferromagnetic layer as separated by the nonmagnetic spacer layer, inwhich the first ferromagnetic layer has a magnetization directiondifferent from the magnetization direction of the second ferromagneticlayer when the applied magnetic field is zero, and the secondferromagnetic layer comprises a pair of ferromagnetic films asantiferromagnetically coupled to each other and a coupling film thatseparates the pair of ferromagnetic films while antiferromagneticallycoupling them, and a nonmagnetic high-conductivity layer adjacent to thefirst ferromagnetic layer on the plane opposite to the plane at whichthe first ferromagnetic layer is contacted with the nonmagnetic spacerlayer.

In the present invention, the magnetoresistance effect device mayrealize extremely high sensitivity while maintaining a good bias point.Preferably, the MR device may be in the form of a so-called spin valvedevice (see U.S. Pat. No. 5,206,590), in which the first ferromagneticlayer is not coupled to the second ferromagnetic layer and themagnetization directions of the two layers are perpendicular to eachother at zero applied magnetic field. Preferably, the applied magneticfield to change the magnetization of the first ferromagnetic layer maybe smaller than that to change the magnetization of the secondferromagnetic layer, and the magnetization of the second ferromagneticlayer is pinned to such a degree that the magnetization direction maynot change even in the presence of an applied magnetic field.

In the present invention, the nonmagnetic high-conductivity layer maycontain an element of which the specific resistance in bulk at roomtemperature is not larger than 10 μΩcm, thereby realizing goodcharacteristic, namely, high MR ratio owing to the spin filter effect inthe ultra-thin first ferromagnetic layer and low Hcu.

For high density recording and for realizing the increase in MR ratioowing to the spin filter effect of the nonmagnetic high-conductivitylayer, the thickness of the first ferromagnetic layer may be between 0.5nanometers and 4.5 nanometers.

In the present invention, the thickness of the nonmagnetichigh-conductivity layer and that of the second ferromagnetic layer maybe so designed that the wave asymmetry, (V1−V2)/(V1+V2), in which V1indicates the peak value of the reproduction output in a positive signalfield and V2 indicates the peak value of the reproduction output in anegative signal field, may fall between minus 0.1 and plus 0.1.

In the present invention, the MR device may satisfy the conditions of0.5 nanometers≦tm(pin1)−tm(pin2)+t(HCL)≦4 nanometers and t(HCL)≧0.5nanometers, in which t(HCL) indicates the thickness of the nonmagnetichigh-conductivity layer (in terms of the Cu layer having a specificresistance of 10 μΩcm), and tm(pin1) and tm(pin2) indicate the magneticthicknesses of the pair of ferromagnetic films, respectively, in thesecond ferromagnetic layer in terms of saturation magnetization of 1Tesla, where pin 1 is of one of the ferromagnetic films disposedadjacent to the nonmagnetic spacer layer and pin2 is of another one ofthe ferromagnetic films. Satisfying the conditions noted above, the MRdevice may realize the wave asymmetry failing between minus 0.1 and plus0.1 and high MR.

In the present invention, the first ferromagnetic layer may have amagnetic thickness, thickness×saturation magnetization, of smaller than4.5 nanometer Tesla.

In the present invention, the nonmagnetic high-conductivity layer may beof a metal film that contains at least one metal element selected fromthe group consisting of copper (Cu), gold (Au), silver (Ag), ruthenium(Ru), iridium (Ir), rhenium (Re), rhodium (Rh), platinum (Pt), palladium(Pd), aluminium (Al), osmium (Os) and nickel (Ni), all of which areadvantageous for meeting the condition of realizing low Hin.

In the present invention, the nonmagnetic high-conductivity layer mayhave a laminate film composed of at least two layers, for attaining lowHin and soft magnetic characteristics control. In the present invention,in the laminate film, the layer adjacent to the first ferromagneticlayer may contain copper (Cu) which is especially suitable for realizinghigh MR ratio, low Hcu and soft magnetic characteristics. In thelaminate film, the layer not adjacent to the first ferromagnetic layermay contain at least one element selected from the group consisting ofruthenium (Ru), rhenium (Re), rhodium (Rh), palladium (Pd), platinum(Pt), iridium (Ir) and osmium (Os) all of which are especially suitablefor realizing low Hin, low Hcu and soft magnetic characteristicscontrol.

In the present invention, the nonmagnetic high-conductivity layer mayhave a thickness of from 0.5 nanometers to 5 nanometers and the elementmay realize low Hcu and high MR ratio.

In the present invention, the layer that is contacted with thenonmagnetic high-conductivity layer at the plane opposite to the planeat which the nonmagnetic high-conductivity layer is contacted with thefirst ferromagnetic layer may contain at least one element selected fromthe group consisting of tantalum (Ta), titanium (Ti), zirconium (Zr),tungsten (W), hafnium (Hf), molybdenum (Mo), and chromium (Cr), and thedevice may realize low Hin and high MR ratio.

In the present invention, the first ferromagnetic layer may be of alaminate film that comprises an alloy layer containing nickel iron(NiFe) and a layer containing cobalt (Co) and the device may realizehigh MR ratio and soft magnetic characteristics.

In the present invention, the first ferromagnetic layer may be an alloylayer containing cobalt iron (CoFe) and the element may realize high MRratio and soft magnetic characteristics.

In the present invention, for pinning the magnetization direction of thesecond ferromagnetic layer, an antiferromagnetic layer may be laminatedover the layer.

In the present invention, for realizing still high MR ratio even afterthermal treatment in its production, the antiferromagnetic layer may bemade of a material, XzMn1-z in which X indicates at least one elementselected from the group consisting of iridium (Ir), ruthenium (Ru),rhodium (Rh), platinum (Pt), palladium (Pd) and rhenium (Re) and thecompositional factor z falls between 5 atm. % and 40 atm. %, in thepresent invention.

In the present invention, the antiferromagnetic layer may be made of amaterial, XzMnl-z in which X indicates at least one element selectedfrom the group consisting of platinum (Pt) and palladium (Pd) and thecompositional factor z falls between 40 atm. % and 65 atm. %, and theelement may maintain high MR ratio.

In the present invention, the nonmagnetic spacer may be of a metal layercontaining copper (Cu) and its thickness maybe between 1.5 nanometersand 2.5 nanometers and the element may realize high MR ratio for moreefficiently utilizing the effect of high MR ratio by the nonmagnetichigh-conductivity layer, and may also realize low Hcu.

In the present invention, the pair of ferromagnetic films asantiferromagnetically coupled to each other may have the same thicknessand the difference in the magnetic thickness, thickness×saturationmagnetization, between the pair of ferromagnetic films may fall between0 nanometer Tesla and 3 nanometer Tesla, and the element may realizehigh MR, improved ESD resistance, and the thermal stability of thesecond ferromagnetic layer.

In the present invention, the antiferromagnetically layer coupling thepair of ferromagnetic films to each other may comprise Ru and itsthickness may fall between 0.8 nanometers and 1.2 nanometers.

In a second aspect, the present invention provides a magnetoresistanceeffect device comprising a nonmagnetic spacer layer, a firstferromagnetic layer and a second ferromagnetic layer as separated by thenonmagnetic spacer layer, in which the magnetization direction of thefirst ferromagnetic layer differs from that of the second ferromagneticlayer when the applied magnetic field is zero, and a nonmagnetichigh-conductivity layer adjacent to the first ferromagnetic layer on theplane opposite to the plane at which the first ferromagnetic layer iscontacted with the nonmagnetic spacer layer, in which the thickness ofthe nonmagnetic high-conductivity layer and the thickness of theferromagnetic layer are so designed that the wave asymmetry,(V1−V2)/(V1+V2), in which V1 indicates the peak value of thereproduction output in a positive signal field and V2 indicates the peakvalue of the reproduction output in a negative signal field, fallsbetween minus 0.1 and plus 0.1.

For attaining the wave asymmetry of falling between minus 0.1 and plus0.1, it may not be always necessary to employ the constitution of SyAFin the device but also a single layer. In that case, it is desirablethat the second ferromagnetic layer of a single layer may have amagnetic thickness of from 0.5 nanometer Tesla to 3.6 nanometer Tesla.If the magnetic thickness of the single layer of the secondferromagnetic layer is larger than 3.6 nanometer Tesla, it may bedifficult to attain the wave asymmetry noted above. On the other hand,if it is smaller than 0.5 nanometer Tesla, the MR ratio in the devicewill be noticeably small.

In a third aspect, the present invention provides a magnetoresistanceeffect device comprising a nonmagnetic spacer layer, first and secondferromagnetic layers separated by the nonmagnetic spacer layer, in whichthe magnetization direction of the first ferromagnetic layer differsfrom that of the second ferromagnetic layer when the applied magneticfield is zero, and a nonmagnetic high-conductivity layer adjacent to thefirst ferromagnetic layer on the plane opposite to the plane at whichthe first ferromagnetic layer is contacted with the nonmagnetic spacerlayer and that the device satisfies the conditions of 0.5nanometers≦tm(pin)+t(HCL)≦4 nanometers and t(HCL)≧0.5 nanometers, inwhich t(HCL) indicates the thickness of the nonmagnetichigh-conductivity layer in terms of copper having a specific resistanceof 10 μΩcm, and tm(pin) indicates the magnetic thicknesses of the secondferromagnetic layer, respectively, in the second ferromagnetic layer interms of saturation magnetization of 1Tesla.

Satisfying the conditions noted above, the MR device may realize thewave asymmetry falling between minus 0.1 and plus 0.1 and high MR, evenwhen the second ferromagnetic layer therein is a single layer.

In a fourth aspect, the present invention provides a magnetoresistanceeffect device comprising a pinned magnetic layer and a free layer asseparated by a nonmagnetic spacer layer disposed therebetween, and anantiferromagnetic layer as laminated on the pinned magnetic layer forpinning the magnetization of the pinned magnetic layer, the pinnedmagnetic layer comprises a pair of ferromagnetic layers, a ferromagneticlayer A as disposed adjacent to the nonmagnetic spacer layer and aferromagnetic layer B as disposed adjacent to the antiferromagneticlayer, that those ferromagnetic layers A and B are antiferromagneticallycoupled to each other via an antiferromagnetically coupling layerexisting therebetween, and that the close-packed plane of theantiferromagnetic layer is so oriented that the half-value width of thediffraction peak from the closed packed plane of the layer in itsrocking curve appears at 8° or smaller.

In a fifth aspect, the present invention provides a magnetoresistanceeffect element comprising a nonmagnetic spacer layer, and first andsecond ferromagnetic layers separated by the nonmagnetic spacer layer, amagnetization direction of the first ferromagnetic layer being at anangle relative to a magnetization direction of the second ferromagneticlayer at zero applied magnetic field, the second ferromagnetic layercomprising first and second ferromagnetic films antiferromagneticallycoupled to one another and an antiferromagnetically coupling filmlocated between and in contact with the first and second ferromagneticfilms for coupling the first and second ferromagnetic films togetherantiferromagnetically so that their magnetizations are alignedantiparallel with one another and remain antiparallel in the presence ofan applied magnetic field, the magnetization of the first ferromagneticlayer freely rotating in signal magnetic field. The element furthercomprises a pair of electrodes coupled to the magnetoresistance effectfilm and having respective inner edges; and a pair of longitudinalbiasing layers for providing bias magnetic fields to the firstferromagnetic layer in parallel with a longitudinal direction of thefirst ferromagnetic layer and having respective inner edges, wherein theinner edges of the pair of electrodes are disposed between the inneredges of the pair of longitudinal biasing layers.

In a sixth aspect, the present invention provides a magnetoresistanceeffect device comprising a spin valve film and a pair of electrodes forsupplying sense current to the spin valve film, in which the spin valvefilm comprises at least one nonmagnetic spacer layer and at least twomagnetic layers as separated by the nonmagnetic spacer layer existingtherebetween. The spin valve film is provided with a magnetoresistanceeffect-improving layer of being a laminate film of a plurality of metalfilms as disposed adjacent to the magnetic layer on the plane oppositeto the plane at which the nonmagnetic spacer layer is contacted with themagnetic layer, and with a nonmagnetic layer acting as a underlayer or aprotecting layer as disposed adjacent to the magnetoresistanceeffect-improving layer on the plane opposite to the plane at which themagnetic layer is contacted with the magnetoresistance effect-improvinglayer, and that the element essentially constituting the metal film ofthe magnetoresistance effect-improving layer that is adjacent to themagnetic layer does not form a solid solution with the elementessentially constituting the magnetic layer.

In the above descried element, the magnetoresistance effect-improvinglayer may exhibit, as its one capability as follows. In the device inwhich the free layer is thin, the magnetoresistance effect-improvinglayer acts as a nonmagnetic high-conductivity layer such as thatmentioned above. In this, the interface between the ultra-thin freelayer and the nonmagnetic high-conductivity layer is formed of acombination of materials not producing a solid solution therein, therebypreventing any diffusive scattering of electrons in the interface so asto improve the up-spin transmittance. With that constitution, the devicemaintains high MR ratio therein. As not having a solid solution phase,the interface is stable to thermal treatment and does not cause thereduction in MR ratio in the device. The magnetoresistanceeffect-improving layer exhibits its ability to improve themagnetoresistance effect of the device, while being based not only onits spin filter capability but also on its additional capabilities tocontrol the microcrystal structure of the spin valve film and to reducethe magnetostriction in the film.

In one specific example, the magnetic layer adjacent to themagnetoresistance effect-improving layer may be made of Co or a Coalloy, the magnetoresistance effect-improving layer may comprise atleast one element selected from Cu, Au and Ag. In another example of thedevice where the magnetic layer adjacent to the magnetoresistanceeffect-improving layer may be made of an Ni alloy, the magnetoresistanceeffect-improving layer may comprise at least one element selected fromRu, Ag, Cu, and Au. In the device, the magnetoresistanceeffect-improving layer may comprise any one or more elements of Cu, Au,Ag, Pt, Rh, Ru, Al, Ti, Zn, Hf, Pd, Ir, etc.

The magnetoresistance effect device of the invention is based on thetechnique of reducing the magnetostriction in the CoFe alloys and othersnoted above by or Au/Cu laminate film, Ru/Cu laminate film, or Au—Cualloys. Specifically, the device comprises a spin valve film and a pairof electrodes for supplying sense current to the spin valve film, inwhich the spin valve film comprises one nonmagnetic spacer layer and twomagnetic layers as separated by the nonmagnetic spacer layer existingtherebetween, and this is characterized in that, of at least twomagnetic layers, one of which the magnetization direction varies,depending on the applied magnetic field, is oriented to fcc(111), andthat the d(111) lattice spacing is between 0.2055 and 0.2035 nanometers.

In a seventh aspect, the present invention provides a magnetoresistanceeffect device comprising a giant magnetoresistance effect film and apair of electrodes for supplying current to the giant magnetoresistanceeffect film, in which the giant magnetoresistance effect film comprisesat least a pair of a pinned magnetic layer and a free layer as separatedby a nonmagnetic spacer layer disposed therebetween, and anantiferromagnetic layer as laminated on the pinned magnetic layer forpinning the magnetization of the pinned magnetic layer, and which ischaracterized in that the pinned magnetic layer comprises a pair offerromagnetic layers, a ferromagnetic layer A as disposed adjacent tothe nonmagnetic spacer layer and a ferromagnetic layer B as disposedadjacent to the antiferromagnetic layer, that those ferromagnetic layersA and B are antiferromagnetically coupled to each other via anantiferromagnetically coupling layer existing therebetween, and that theantiferromagnetic layer has a thickness of at most 20 nanometers and hasa magnetic coupling coefficient, J, for the ferromagnetic layer B of atleast 0.02 erg/cm² at 200° C.

In an eighth aspect, the present invention provides a magnetoresistanceeffect element comprising a giant magnetoresistance effect film and apair of electrodes for supplying current to the giant magnetoresistanceeffect film, in which the giant magnetoresistance effect film comprisesat least a pair of a pinned magnetic layer and a free layer as separatedby a nonmagnetic spacer layer disposed therebetween, and anantiferromagnetic layer as laminated on the pinned magnetic layer forpinning the magnetization of the pinned magnetic layer, the pinnedmagnetic layer comprises a pair of ferromagnetic layers, a ferromagneticlayer A as disposed adjacent to the nonmagnetic spacer layer and aferromagnetic layer B as disposed adjacent to the antiferromagneticlayer, those ferromagnetic layers A and B are antiferromagneticallycoupled to each other via an antiferromagnetically coupling layerexisting therebetween, and the antiferromagnetic layer has a thicknessof at most 20 nanometers and contains at least any one of Z_(x)Mn_(1-x)(where Z is at least one selected from Ir, Rh, Ru, Pt, Pd, Co and Ni,and 0<×<0.4), Z_(x)Mn_(1-x) (where Z is at least one selected from Pt,Pd and Ni, and 0.4≦×≦0.7), or Z_(x)Cr_(1-x) (where Z is at least oneselected from Mn, Al, Pt, Pd, Cu, Au, Ag, Rh, Ir and Ru, and 0<×<1).

The magnetic head and the magnetic recording/reproducing system of theinvention incorporate the magnetoresistance effect device of theinvention noted above. Specifically, the magnetic head of the inventionis characterized by comprising a lower magnetic shield layer, amagnetoresistance effect device of the invention such as that notedabove, which is formed on the lower magnetic shield layer via a lowerreproducing magnetic gap therebetween, and an upper magnetic shieldlayer as formed on the magnetoresistance effect device via an upperreproducing magnetic gap therebetween.

The magnetic head for separated recording/reproducing of the inventionis provided with a reproducing head that comprises a lower magneticshield layer, a magnetoresistance effect device of the invention such asthat noted above, which is formed on the lower magnetic shield layer viaa lower reproducing magnetic gap therebetween, and an upper magneticshield layer as formed on the magnetoresistance effect device via anupper reproducing magnetic gap therebetween, and with a recording headthat comprises a lower magnetic pole which is common to the uppermagnetic shield layer, a recording magnetic gap as formed on the lowermagnetic pole, and an upper magnetic pole as formed on the recordingmagnetic gap.

The magnetic head assembly of the invention is characterized bycomprising a head slider having the separated recording/reproducingmagnetic head of the invention noted above, and an arm having asuspension on which the head slider is mounted. The magneticrecording/reproducing system of the invention is characterized bycomprising a magnetic recording medium, and a head slider provided withthe separated recording/reproducing magnetic head of the invention notedabove with which signals are written on the magnetic recording medium ina magnetic field and signals are read in the magnetic field as generatedby the magnetic recording medium.

The magnetoresistance effect device of the invention mentioned above isapplicable not only to magnetoresistance effect heads but also tomagnetoresistance effect sensors.

Any one of the present invention may be provided not only in disc drivesystem but also other magnetic storage system, such as magnetic memorydevice. The magnetic disc drive system of the invention is characterizedin that a current is applied to the magnetoresistance effect device inthe magnetoresistance effect head to generate a magnetic field and thatthe system is provided with a mechanism capable of pinning themagnetization of the pinned magnetic layer in a predetermined directionin the thus-generated magnetic field.

Method for producing the magnetoresistance effect elements of theinvention comprises heating the pair of ferromagnetic film A and theferromagnetic film B of the synthetic pinned layer in a magnetic field,after the film of the giant magnetoresistance effect device has beenformed but before it is patterned, thereby pinning the magnetization ofthe pinned magnetic layer in a predetermined direction.

BRIEF DESCRIPTION OF THE DRAWINGS

A more complete appreciation of the invention and many of the attendantadvantage thereof is readily obtained as the same becomes betterunderstood by reference to the following detailed description whenelectrode in connection with the accompanying drawings, wherein:

FIG. 1 is a sectional view for explaining the film constitution of thefirst magnetoresistance effect device of the invention.

FIG. 2 is a transfer curve given by the first magnetoresistance effectdevice of the invention.

FIG. 3 is a graph of the Cu thickness of the high-conductivity layeradjacent to the free layer on the side opposite to the side at which thespacer is contacted with the free layer, versus the current magneticfield Hcu applied to the free layer.

FIG. 4 is a graph concretely showing the range of the pinned layerthickness and the nonmagnetic high-conductivity layer thickness forrealizing asymmetry of from −10% to +10%, or that is, for realizing biaspoints of from 30% to 50%.

FIG. 5 is a sectional view of a typical film constitution of the firstembodiment of the magnetoresistance effect device of the invention.

FIG. 6 is a sectional view of a film constitution of the spin valve filmof one example of the invention.

FIG. 7A and FIG. 7B are conceptual views for explaining two problemswith conventional magnetoresistance effect devices.

FIG. 8 is a graph of calculated bias point values versus headreproducing signal waves.

FIG. 9 is an explanatory view indicating magnetic fields acting on afree layer.

FIG. 10 is a sectional view of a magnetoresistance effect film, in whichare shown current flows I₁ to I₃ running through the layers.

FIG. 11 is a conceptual view showing the condition of the bias point inComparative Case 1.

FIG. 12 is a conceptual view of the bias point versus Hin, Hpin and Hcuon a transfer curve.

FIG. 13 is a conceptual view showing the determinant factors for thebias point in Comparative Case 3.

FIG. 14 is a conceptual view showing the determinant factors for thebias point in Comparative Case 4.

FIG. 15 is a graph of the free layer thickness dependence of the biaspoint in the spin valve films of the invention, as compared with that inthe spin valve films of Comparative Cases.

FIG. 16 is a graph of the MR ratio in the structures of ComparativeCases 1 to 4 with the product of Ms×t only in the free layer beingreduced.

FIG. 17 is a sectional view of one embodiment of the magnetoresistanceeffect head of the invention.

FIG. 18 is a schematic view of the magnetic coupling bias field HUA*versus the change in the resistance, R, of the spin valve film dependingon the applied magnetic field.

FIG. 19 is a graph of the angle of movement of the magnetization of thepinned magnetic layer, versus time, in the presence of a simulation biasfield.

FIG. 20 shows the data of the half-value width of the diffraction peakfrom the close-packed plane of an antiferromagnetic layer in its rockingcurve.

FIG. 21 is a graph of residual magnetization ratio, Mr/Ms, indicatingthe reduction in the antiferromagnetic coupling capability of theantiferromagnetically coupling layer of Ru after thermal treatment,relative to the thickness of the Ru layer.

FIG. 22A, FIG. 22B and FIG. 22C are graphs of resistance change in spinvalve films versus the applied magnetic field.

FIG. 23A, FIG. 23B and FIG. 23C are graphs of resistance change in spinvalve films with the thicknesses of the ferromagnetic layer A andferromagnetic layer B being varied, versus the applied magnetic field.

FIG. 24A and FIG. 24B are graphs of resistance versus output in a spinvalve device to which has been applied a simulation ESD voltage by ahuman body model.

FIG. 25A and FIG. 25B are graphs of resistance versus output in anotherspin valve device to which has been applied a simulation ESD voltage bya human body model.

FIG. 26 is a perspective view of a spin valve film, indicating the straymagnetic field from the film.

FIG. 27 is a sectional view of another embodiment of themagnetoresistance effect head of the invention.

FIG. 28 is a sectional view of still another embodiment of themagnetoresistance effect head of the invention.

FIG. 29 is a sectional view of still another embodiment of themagnetoresistance effect head of the invention.

FIG. 30 is a sectional view of still another embodiment of themagnetoresistance effect head of the invention.

FIG. 31 is a sectional view of still another embodiment of themagnetoresistance effect head of the invention.

FIG. 32 is a sectional view of the essential structure of one embodimentof the magnetoresistance effect device of the invention.

FIG. 33 is a sectional view of one modification of the embodiment of themagnetoresistance effect device of FIG. 32.

FIG. 34 is a sectional view of another modification of the embodiment ofthe magnetoresistance effect device of FIG. 32.

FIG. 35A, FIG. 35B and FIG. 35C are views showing the reduction in theMR ratio in conventional spin valve films after thermal treatment.

FIG. 36 is a view explaining specular reflection on metal/metalinterface.

FIG. 37A and FIG. 37B are graphs showing two examples of therelationship between the ratio of the Fermi wavelength in a reflectivefilm to the Fermi wavelength in a GMR film adjacent to the reflectivefilm, and the critical angle θc.

FIG. 38 is a graph of the data of the critical angle θc at which Au(Ag)/Cu interface produces specular reflection, as calculated from theFermi wavelength at the interface.

FIG. 39 is a sectional view of still another modification of themagnetoresistance effect device of FIG. 32.

FIG. 40 is a sectional view of one modification of the magnetoresistanceeffect device of FIG. 39.

FIG. 41 is a sectional view of the essential part of the secondembodiment of the magnetoresistance effect device of the invention.

FIG. 42 is a sectional view of one modification of the magnetoresistanceeffect device of FIG. 41.

FIG. 43 is a sectional view of the essential part of the thirdembodiment of the magnetoresistance effect device of the invention.

FIG. 44 is a sectional view of the structure of the first embodiment ofa separated recording/reproducing magnetic head which incorporates themagnetoresistance effect device of the invention.

FIG. 45 is a sectional view of the structure of the second embodiment ofa separated recording/reproducing magnetic head which incorporates themagnetoresistance effect device of the invention.

FIG. 46 is a perspective view of the structure of one embodiment of amagnetic head assembly which incorporates the separatedrecording/reproducing magnetic head of the invention.

FIG. 47 is a perspective view of the structure of one embodiment of amagnetic disc system which incorporates the separatedrecording/reproducing magnetic head of the invention.

FIG. 48 is a graph of an XRD pattern of the spin valve film as producedin Example 1 of the invention.

FIG. 49 is a sectional view of the essential part of one embodiment ofan artificial lattice film which incorporates the magnetoresistanceeffect device of the invention.

FIG. 50 is a conceptual view showing the cross section of a spin valvedevice part as seen from its ABS (air baring surface). ABS may comprisea protective film formed thereon.

FIG. 51 is a perspective view of a spin valve device with its gap filmand shield film being removed.

FIG. 52 is a conceptual view of one embodiment of a head which issuitable to the top-type spin valve film of FIG. 1 and FIG. 5.

FIG. 53 is a graph of the data of nano-EDX analysis of the cross sectionof a magnetic head which incorporates the magnetoresistance effectdevice of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Embodiments of the invention are described in detail hereunder withreference to the drawings.

First Embodiment

First mentioned is the embodiment of the invention in which the freelayer (first ferromagnetic layer) is thinned.

The problems with the technique of “thinning the free layer” which thepresent inventors have recognized in the process of achieving thisembodiment of the invention are described in detail.

As so mentioned hereinabove, remarkable increase in the sensitivity ofmagnetoresistance effect devices is realized not only by increasing theMR ratio but also by reducing the thickness of the free layer (that is,by reducing the product of Ms×t). In a broad way, the output increases,being in reverse proportion to the product of Ms×t of the free layer.However, the present inventors own investigations have verified that thetechnique of thinning the free layer brings about the followingproblems.

The first problem is that the bias point designing in an applied sensecurrent is difficult. When all the magnetic fields applied to the freelayer being driven are summed up and when the bias point is in thecenter of the linear inclination of a transfer curve, the biasingcondition will be the best. However, when the free layer is thinned, theinclination of the transfer curve becomes steep. In that condition, itis extremely difficult to lead the bias point to the center of thelinear region of the transfer curve. In a bad bias point condition,asymmetric signals will be formed, and in a worse condition, no outputlevel could be taken.

The second problem is that, if the free layer is thinned to an extremedegree according to a prior art technique, the MR ratio is greatlylowered. The reduction in the MR ratio causes the reduction in thereproducing output.

FIG. 7A and FIG. 7B are conceptual views for explaining the two problemswith conventional magnetoresistance effect devices. In those drawings,shown are the transfer curves of magnetic heads each having amagnetoresistance effect device. FIG. 7A shows one case where the freelayer is thick; and FIG. 7B shows another case where the free layer isthin. As mentioned above, when the free layer is thinned, theinclination of the transfer curve becomes steep (that is, Hs becomessmall), and the MR ratio decreases. As a result, AV becomes small. FromFIG. 7A and FIG. 7B, known are the two problems noted above.

Of the two problems, one relating to the bias point could not berecognized with ease even though the film structure is determined.Therefore, film structure designing was extremely difficult. This time,we, the present inventors carried out various simulations, and correctedthe errors in the data we obtained, on the basis of our experiences. Asa result, we have succeeded in correct judgment of the bias point. Thecalculation of the bias point is mentioned below.

The bias point is shifted by various external magnetic fields applied tothe free layer. The shift could approximate the sum total of (1) currentmagnetic field (Hcu), (2) the static magnetic field from the pinnedlayer (Hpin), (3) the interlayer coupling magnetic field from the pinnedlayer via a spacer (Hin), and (4) the stray magnetic field (Hhard) fromthe hard bias film for the purpose of imparting a longitudinal bias tothe magnetoresistance effect film. Of those magnetic fields (1) to (4),the hard bias magnetic field (4) is relatively small. Having noted thesum of the magnetic fields (1) to (3), we, the present inventors haveassiduously studied. The calculation formulae for the bias point whichwe employed this time are mentioned below.B.P.=50×(Hshift/Hs)+50  (1-1)Hshift=−Hin+Hpin±Hcu  (1-2)Hs=Hd ^(free) +Hk  (1-3)Hd ^(free)=π²(Ms×t)_(free) /h  (1-3-1)Hpin=π²(Ms×t)_(pin) /h  (1-4)Hcu=2πC×I _(s) /h  (1-5)C=(I ₁ −I ₃)/(I ₁ +I ₂ +I ₃)  (1-5-1)

B.P. to be represented by the formula (1-1) is the bias point [%] to bespecifically noted herein. The best bias point is 50%. Including themargin, the practicable range of the bias point will fall between 40 and60%. If the bias point oversteps the range, asymmetric signals will beformed. In worse cases, no output could be obtainable.

Regarding the relationship between the bias point value and theasymmetry, the asymmetry will be +10% or so when the bias point is 40%,and it will be −10% or so when the bias point is 60%. As will bementioned hereunder, the best bias point in calculation does not fallbetween 40 and 60%, but falls between 30 and 50% in experiences.

FIG. 8 is a graph of calculated bias point values versus headreproducing signal waves. As shown, when the bias point falls between 30and 50%, the asymmetry is relatively small, and the signal profiles aregood. However, when the bias point is outside the range, the asymmetrybecomes great, as in FIG. 8, and the signal profiles are notpracticable.

As in the formula (1-2), Hshift, is the sum of the magnetic fields [Oe]applied to the free layer. As in FIG. 7, Hs is the inclination of thetransfer curve.

FIG. 9 is an explanatory view indicating magnetic fields acting on thefree layer.

Hd^(free) is an antimagnetic field for the free layer at a certain MRheight h is the MR height [μm]. Hpin is the pinned layer stray magneticfield from the pinned layer to the free layer. (Ms×t)_(free) is theproduct of the total saturation magnetization, Ms, and the thickness, t,of the free layer. (Ms×t)_(pin) is the product of the saturationmagnetization and the thickness of the net pinned layer (for SyntheticAF, the difference in the magnetic thickness between the upper and lowerpinned layers).

Hcu is the current magnetic field applied to the free layer. Is is thesense current [mA]. The coefficient, C, in the formula (1-5-1) is theratio of the partial current flow running through the upper layeroverlying the free layer to that running through the lower layerunderlying it.

FIG. 10 is a conceptual view indicating the partial current flows I₁ toI₃ running through the layers.

For simplifying the calculation, the influences of the edges of the ABSplane and those of shields are not taken into consideration. In ourexperiences, we, the present inventors have found that the bias pointvalues as estimated in calculation are shifted to the minus side byabout 10% from those in actual heads. Considering the fact that theusable bias point range falls plus/minus 10% of the best bias pointvalue, it can be said that the good bias point range will fall between30% and 50% to be obtained in calculation. Accordingly, when the biaspoint falls between 30% and 50%, as obtained according to thecalculation shown above, it could be judged that the bias point valueswithin the range are good for practical use.

The problems with some conventional spin valve films are described indetail hereunder, with reference to the bias point calculation formulaementioned above.

Comparative Case 1: ordinary spin valve (with neither high-conductivityfilm nor Synthetic AF)5 nanometer Ta/2 nm NiFe/0.5 nm Co/2 nm Cu/2 nm CoFe/7 nm IrMn/5nanometer Ta  (1)

The formula (1) indicates the laminate structure of the spin valve, inwhich are shown the elements constituting the layers and theirthicknesses (nanometers). The film of this Comparative Case is amodification of a prior art spin valve film in which only the free filmis thinned. The bias points in this film constitution are calculated.

Of the bias point formulae (1-1) to (1-5) noted above, the currentmagnetic field of the formula (1-5) is the most difficult to obtain.This is because the current flow ratio, C, of the formula (1-5-1) isdifficult to obtain. In the thinned film, the specific resistance ofeach layer is influenced by the crystallinity and the currentdistribution, and significantly differs from the specific resistance ofthe bulk. For practicable calculation as much as possible, we, thepresent inventors took the following measure and succeeded in obtainingthe accurate current flow ratio, C.

For obtaining the specific resistance of each layer, a spin valve filmsample having the constitution noted above is prepared. For obtainingthe specific resistance of a predetermined layer, a few samples in whichthe thickness of the layer is varied by plus/minus 2 nanometers areprepared. In those samples, the relationship between the thickness ofthe layer and the conductance is obtained through linear extrapolation.The reason for the process is because actual data could not be obtainedaccording to the well-known technique of obtaining the specificresistance of thin, single-layer films. In order to minimize theinfluences of crystallinity and those of current distribution, we, thepresent inventors have found through our experiments that the best wayfor accurate determination is to prepare film samples in which even theoverlying and underlying layers are of practicable materials and todetermine the conductance difference within the small thickness range asmentioned above.

The specific resistance of each layer as obtained according to themethod is influenced little by the crystallinity and, in addition, couldcancel the influences of current distribution thereon. Therefore, thedata of the current flow ratio, C, of the formula (1-5-1) obtainedaccording to this method are much more accurate than those obtained in asimple conductor in which is used the specific resistance ofsingle-layer films. According to the method, it has become possible tocalculate and estimate the current magnetic field with high accuracy,which, however, is difficult in the prior art technique.

The data of the specific resistance of each layer as obtained accordingto the method mentioned above are as follows: NiFe has 20 μΩcm; CoFe 13μΩcm; spacer Cu 8 μΩcm; IrMn 250 μΩcm. If the underlayer of Ta(tantalum) is thick, its specific resistance will greatly vary throughcrystallization. The cap Ta is much influenced by the surface oxides.Therefore, their accurate data could not be obtained. The specificresistance of the Ta layer is presumed to be 100 μΩcm. Based on thosedata, the current flow ratio of each layer is obtained, and the currentmagnetic field Hcu is calculated according to the formula (1-5).

The value of Hin is 25 Oe, as measured. Hpin is obtained according tothe formula (1-4).

In the film constitution of this case, the height is shortened while thethickness of the pinned layer is thick. Therefore, the stray magneticfield, Hpin, from the pinned layer to the free layer is large. Inaddition, since more current flows above the free layer than below it,the current magnetic field Hcu applied to the free layer is large.Accordingly, for designing the bias point, it maybe employable tocontrol the bias point by canceling the large Hpin by the large currentmagnetic field Hcu.

The bias point values as calculated on the basis of the data obtainedabove are shown in Table 1. The sense current is 4 mA.

TABLE 1 Calculated Bias Point in Film of Comparative Case 1 MR height[micrometers] Bias Point 0.3 70% 0.5 61% 0.7 53%

As is known from Table 1, the bias point falls between 61 and 70% whenthe MR height falls between 0.3 and 0.5 micrometers, and this overstepsthe calculated best bias point range.

FIG. 11 is a conceptual view showing the condition of the bias point inComparative Case 1. It is understood that reducing the MR height resultsin shifting of the bias point to the antiferromagnetic site (to the sitelarger than 50%). The MR height inevitably fluctuates, owing to themechanical polishing. It is understood-that the MR height distributionlowers the yield. Qualitatively, the reason is because the bias point iscontrolled in the extremely unstable method where the large pinned layerstray magnetic field Hpin is canceled by the large current magneticfield Hcu.

Except for the bias point, the film of this Comparative Case has stillanother essential problem. The problem is that the ultra-thin free layerto which the present invention is directed lowers the MR ratio. Throughour experiments, we, the present inventors have found the fact that theMR ratio in the devices having a thinned free layer is extremely loweredafter thermal treatment, and this is a serious problem with the devices.For example, in the film constitution of Comparative Case 1, the MRratio in the as-deposited condition is around 11%, but is 5.6% afterthermal treatment. That is, the latter is about a half of the former. Inthat condition, spin valve films practicable in high-densityrecording/reproducing systems could not be realized.

In the spin valve film of this Comparative Case, the layers are allthinned, and the sheet resistance of the film is around 30 Ω, and islarge. In view of the electrostatic discharge (ESD), the film is notpracticable. As well known, ESD increases with the increase in theresistance.

From the above, it is understood that the film of Comparative Case 1 isnot practicable at all in high-density recording heads.

Comparative Case 2: U.S. Pat. No. 5,422,591 (with spin filter but noSynthetic AF)5 nanometer Ta/x nm Cu/1.5 nm NiFe/2.3 nm Cu/5 nm NiFe/11 nm FeMn/5nanometer Ta  (2)

In order to improve MR in the ultra-thin free layer therein, a spinvalve film has been proposed, in which a high-conductivity layer islaminated on the free layer at the side opposite to the side of thenonmagnetic spacer layer. For example, referred to are U.S. Pat. Nos.2,637,360, 5,422,591 and 5,688,605.

The film (2) is an example of the spin valve film based on U.S. Pat. No.5,422,591. In this spin valve film, the Cu layer adjacent to the freelayer at the side opposite to the side of the spacer Cu is thickened,whereby the mean free path for up-spin is prolonged to increase the MRratio. However, if the Cu layer is too much thickened over the mean freepath, it will be a simple shunt layer. Therefore, in this film, the MRratio peak appears at a certain Cu layer thickness. Based on thisphenomenon, one problem with the film of Comparative Case 1, that is,the reduction in the MR ratio owing to the ultra-thin free layer couldbe overcome in some degree.

However, the film constitution of the spin valve film (2) based on U.S.Pat. No. 5,422,591 has two problems. One is the problem with the biaspoint, and the other is the problem with the thermal stability for theMR ratio.

First, regarding the viewpoint of the bias point, U.S. Pat. No.5,422,591 has no disclosure of direct description or indirectsuggestion. The constitution of the film (2) could not be used at all inpractical heads. The reasons are mentioned in detail hereunder.

In the same manner as in Comparative Case 1, the current magnetic field,Hcu, is obtained on the basis of the experimental data of the specificresistance of each layer. In this case, the specific resistance of Ta ispresumed to be 100 μΩcm, and the experimental data of FeMn, NiFe, spacerCu and subbing Cu are 250 μΩcm, 20 μΩcm, 8 μΩcm and 10 μΩcm,respectively. The sense current is 4 mA. Though not described in U.S.Pat. No. 5,422,591, Hin has been found to fall between 15 Oe and 25 Oethrough our experiments. In this case, Hin is 20 Oe.

The bias point is calculated for high-density recording heads for whichthe size of the device is as follows: track width=0.5 μm, MR height=0.3to 0.5 μm. The data are in Table 2.

TABLE 2 Calculated Bias Point in the Constitution of Comparative Case 2in which the subbing Cu thickness is varied MR height Cu (0 nm) Cu (1nm) Cu (2 nm) 0.3 μm 126% 143% 156% 0.5 μm 111% 127% 140%

In this constitution, the pinned layer stray magnetic field from thepinned layer to the free layer is extremely large, and the bias point isreadily shifted to the plus side. As is known from the data of the biaspoint in Table 2, in the samples with no spin filter effect in which thesubbing Cu thickness is zero, the bias point falls between 111% and 126%at the MR height of from 0.3 to 0.5 μm. This means that the samplesproduce no output. This situation gets worse when the subbing Cu layerthickness is thick as shown in table 2.

FIG. 12 is a conceptual view of the bias point versus Hin, Hpin and Hcuon a transfer curve. As Hpin is large, the bias point oversteps thelevel when the current is zero. This constitution is so designed thatthe bias point is forcedly reduced to 50% by means of an applied currentmagnetic field. In this constitution, however, since the underlayer is ahigh-conductivity layer of Cu, I₃ in FIG. 10 shall be large and thecurrent magnetic field, Hcu, to be obtained according to the formula(1-5) shall be small. In other words, the bias point controlling methodis to cancel the large Hpin by the small Hcu that is opposite directionto Hpin, which is impossible to attain a good bias point value. It isfurther known from Table 2 that the increase in the subbing Cu thicknessresults in further increase in the bias point.

Through our experiments mentioned above, we, the present inventors havefound that the bias point designing is quite difficult in theconstitution of U.S. Pat. No. 5,422,591, and that forming thehigh-conductivity Cu layer as the underlayer of the comparative casemakes the bias point more impracticable.

From the viewpoint of the thermal stability for the MR ratio, the filmof U.S. Pat. No. 5,422,591 is not a practical one. As so described incomparative case, the MR ratio in the as-deposited film surely increasesowing to the spin filter effect. However, after the thermal treatmentfor head fabrication, we, the present inventors have found that the MRratio in the film of the comparative case is greatly reduced as thephenomenon peculiar to ultra-thin free films. This is a serious problem,if high output for high-density recording is intended.

In fact, the MR ratio in the as-deposited film of one example of U.S.Pat. No. 5,422,591 (this is film (2)) is 1.8% when the subbing Cuthickness is 1 nanometer. However, after the thermal treatment in oursimulation, the MR ratio in the U.S. Pat. No. 5,422,591 lowered to 0.8%.As will be mentioned hereunder, the reason for the MR ratio reductionwill be essentially because of the antiferromagnetic film of FeMn inU.S. Pat. No. 5,422,591. Even if the ultra-thin free layer, with whichit is difficult to realize high MR, is used in the spin valve film so asto forcedly increase the MR ratio in the film owing to the spin filtereffect, the film will be quite useless in practical applications. It isunderstood from the data noted above that the simple spin filter effectcould not realize spin valve films having an ultra-thin free layer andexhibiting high MR ratio.

Comparative Case 3: JP-A 10-2612095 nanometer Ta/3 nm Cu/1 nanometer Ta/5 nm NiFe/2.5 nm Cu/2.5 nm Co/10nm FeMn/5 nanometer Ta  (3)

In the film (3) disclosed in JP-A 10-261209, the Cu shunt layer disposedadjacent to the free layer via Ta therebetween is, being different fromthe layer as intended for the spin filter effect for the MR ratio as inU.S. Pat. No. 5,422,591 of Comparative Case 2, intended for stabilizingthe asymmetry by reducing the current magnetic field Hcu and byretarding the bias point fluctuation owing to sense current. This ideawill be effective in the region where the free layer is relatively thickas in the film (3), but is quite ineffective in the case of ultra-thinfree layers to which the present invention is directed, in view of thebias point and the MR ratio. Based on this idea, practicable filmshaving an ultra-thin free layer could not be obtained at all. Thereasons are mentioned below.

First, regarding the bias point, when Hs is extremely reduced by the useof the ultra-thin free layer, as in the film (2) of Comparative Case 2,the best bias point could not be realized even though the currentmagnetic field Hcu is reduced, if the pinned layer stray magnetic fieldis large. The advantage of the structure of the film (3) is that, whenthe free layer is thick, or that is, when Hs is relatively large, thenthe best bias point having been once obtained depends little on thesense current. However, when the free layer in the film constitution of(3) is much reduced, it is naturally impossible to realize the best biaspoint. In other words, when the thickness of the free layer in the filmconstitution of (3) is reduced to 4.5 nanometers or smaller so as tomake the free layer applicable to high-density recording systems, thebias point shall be shifted to the plus side.

To verify the fact, the calculated bias point data of the filmconstitution are shown in Table 3.

TABLE 3 Bias Point in Film of Comparative Case 3 MR height NiFe 5 nmNiFe 3 nm 0.3 μm 86% 108% 0.5 μm 83% 104% 0.7 μm 81% 100%

Hin for the data calculation is 10 Oe. As in Table 3, it is understoodthat the bias point in the film constitution of Comparative Case 3 isnaturally shifted to the plus side even when the thickness of the NiFefilm therein is 5 nanometers, and the film constitution is not welldesigned. In this, the bias point is much more shifted to the plus sidewhen the thickness of the free layer of NiFe is thinned to be 3nanometers.

FIG. 13 is a conceptual view showing the determinant factors for thebias point in Comparative Case 3. As illustrated, since the currentmagnetic field Hcu only is reduced while Hpin is still large, no biaspoint is obtained at all in the region where the free layer is thick.Specifically, since the best bias point appears at the site where thetotal sum of the current magnetic field Hcu, the interlayer couplingmagnetic field Hin and the pinned layer stray magnetic field Hpin iszero, the film designing of such that the current center is made nearerto the free layer while only the current magnetic field is made zero, asin the constitution of (3), is quite meaningless.

The second problem with the constitution of (3) is that the film (3)could not have high MR ratio necessary for high-density recording.Specifically, in the constitution of (3), since a diffusion-preventinglayer of a material having a relatively high resistance is put betweenthe high-conductivity layer and the free layer, the film (3) could notenjoy the spin filter effect for MR, such as that in U.S. Pat. No.5,422,591 noted above, when the free layer is an ultra-thin one. In theregion where the free layer has a thickness of at most 4.5 nanometersand where the present invention is especially effective, as will bedescribed in detail hereunder, the film (3) will be useless as the MRratio therein is lowered.

For the two reasons mentioned above, the idea of the film constitution(3) is exclusively for the region where the free layer is relativelythick, and it is understood that the idea is useless in preparingpracticable films having an ultra-thin free layer.

Comparative Case 4: Synthetic AF with no spin filter5 nanometer Ta/2 nm NiFe/0.5 nm CoFe/2 nm Cu/2.5 nm CoFe/0.9 nm Ru/2 nmCoFe/7 nm IrMn/5 nanometer Ta  (4)

In this Comparative Case, employed is a Synthetic AF structure for thepurpose of improving the pinning characteristics. The two ferromagneticlayers are antiferromagnetically coupled to each other via Ru(ruthenium). One of the two ferromagnetic layers is pinned to the othervia an antiferromagnetic layer existing therebetween. Even if theuni-directionally anisotropic magnetic field Hua is too small fornormally pinned structures, but if it is on a certain level, such asmall Hua is applicable to the Synthetic AF structure, and the pinningresistance of the Synthetic AF structure is high. As previouslymentioned hereinabove, in the Synthetic AF structure, the magnetizationdirections of the upper and lower ferromagnetic layers as coupled via Ruare opposite to each other, and the coupling magnetic field is severalkOe and is much larger than the medium magnetic field for headoperation. Approximately for the magnetic moment running outward,therefore, it is considered that the difference in Ms×t between theupper and lower pinned layer will be equal to the net moment.Specifically, it is possible to reduce the influence of the magneticfield strayed from the pinned layer to the free layer, and it isexpected that the reduction is advantageous for the bias point (see U.S.Pat. No. 5,465,185).

For example, in this Comparative Case, it is considered that the netpinning thickness will be equivalent to the pinned layer having athickness of 0.5 nanometers, and it is possible to realize the pinnedlayer stray magnetic field equivalent to the thin pinned layer, which,however, could not be realized in normal pinning structures. Ideally,when the upper and lower pinned layers are controlled to have the sameproduct of Ms×t, then the pinned layer stray magnetic field could bezero. It has heretofore been considered that only the reduction in thepinned layer stray magnetic field will be satisfactory for good biaspoint designing for spin valve films for high-density recording. Thistime, however, we, the present inventors have found that, if only theSynthetic AF structure is employed, it is impossible to realize stablebias points in ultra-thin free layers applicable to high-densityrecording. The matters we have found are described in detail hereunder.

FIG. 14 is a conceptual view showing the determinant factors for thebias point in this Comparative Case 4. Specifically, in the constitutionof this Comparative Case, the free layer is positioned, being much farfrom the current center of the current distribution in the spin valvefilm. In this, therefore, the current magnetic filed Hcu is extremelylarge. Hin is at most 20 Oe or so, and the pinned layer stray magneticfield is extremely reduced owing to the Synthetic AF structure employed.This means that the film constitution of this Comparative Case 4 isnearly in the just bias condition in the absence of current. Whencurrent is applied to the spin valve film of this constitution, and whenthe applied current is increased, then the film will much overstep thejust bias condition owing to the increased current magnetic field Hcu.

The calculated bias point data of this Comparative Case are shown inTable 4.

TABLE 4 Calculated Bias Point Data of Film of Comparative Case 4 MRheight Hcu↑Hpin↑ Hcu↓Hpin↓ 0.3 μm 88% 22% 0.5 μm 80% 16% 0.7 μm 73% 10%

Hin is 20 Oe. As so anticipated, it is understood from Table 4 that thebias point could not fall the range of from 30 to 50% irrespective ofthe direction of the current flow.

For obtaining the just bias in this constitution, one means may be takeninto consideration, which comprises minimizing as much as possible thepinned layer stray magnetic field, or that is, making the upper andlower pinned layers have the same thickness in the Synthetic AFstructure thereby to make the pinned layer stray magnetic field nearlyzero. It further comprises enlarging Hin as much as possible so that thejust bias could be in the current magnetic field for canceling theenlarged Hin. However, this means is undesirable. The enlarged Hin hassome negative influences on external magnetic field response. Theenlarged Hin shifts the linear region of the response and, in addition,reduces it. It will be good to control Hin to be small. However,fabricating spin valve films while the value is forcedly controlled tobe an unnaturally large and constant one is extremely difficult in massproduction and is unfavorable.

Since no high-conductivity layer is provided on the free layer at theside opposite to the side of the spacer adjacent to the free layer, theMR ratio is lowered when the free layer is an ultra-thin one, for thesame reasons as in Comparative Case 1. Therefore, the film constitutionof this Comparative Case 4 could not ensure satisfactory output, whenapplied to high-density recording heads. This is the essential problemwith this film constitution.

For the two reasons of bias point and high output mentioned above, thespin valve film merely incorporating the Synthetic AF constitution couldnot realize the use of ultra-thin free layers therein for high-densityrecording.

As has been described in detail hereinabove, we, the present inventorshave clarified, through many simulations in various current magneticfields, that the film structures of Comparative Cases 1 to 4 could notattain stable bias point and satisfactorily high output for spin valvefilms having an ultra-thin free layer for high-density recording.Through further studies and investigations, we have achieved the presentinvention. The constitution of the invention is described in detailhereunder.

FIG. 15 is a graph of the free layer thickness dependence of the biaspoint in the spin valve films of the invention, as compared with that inthe spin valve films of the above-mentioned Comparative Cases. It isunderstood that the spin valve films of the Comparative Cases are allproblematic in the bias point. The best bias point for spin valve filmsfalls between 30 and 50%. For satisfactorily high sensitivity, the biaspoint must fall within the defined range at a low Ms×t free layer.

However, the bias point in the Comparative Cases significantly overstepsthe preferred range in the condition of low Ms×t. In addition, in theComparative Cases, the bias point fluctuation relative to Ms×t isextremely large, and it is understood that the bias point is difficultto control in those Comparative Cases.

As opposed to the films of the Comparative Cases, it is understood that,in the film of Example 1 of the invention, the bias point fluctuation isextremely small relative to Ms×t, and the bias point is all the timewithin the preferred range.

In FIG. 15, the calculated bias point values in Comparative Case 1 donot fall within the range between 30% and 50% even in the region whereMs×t is not smaller than 5 nanometer Tesla. This is because, in theactual region of low recording density for which a free layer havingMs×t of at least 5 nanometer Tesla is used, the MR height is large.Concretely, this is because the MR height for low recording densityheads is larger than the range of from 0.3 μm to 0.5 μm for the highrecording density to which the present invention is directed.

Anyhow, it is obvious that, in the region where Ms×t is at most 5nanometer Tesla, the bias point designing for the films of the inventionis much superior to that for the films of the Comparative Cases.

FIG. 16 is a graph of the MR ratio in the structures of ComparativeCases 1 to 4 with the product of Ms×t only in the free layer beingreduced. In this, the MR ratio as plotted in the vertical axis is nearlyproportional to the vertical axis of FIG. 9 for the transfer curve. Forcomparison, the data of Examples 1 and 2 of the invention to bementioned hereunder are also plotted in FIG. 16.

The film samples of Comparative Cases 1 to 4 and those of Example 1 ofthe invention were prepared, in which the thickness of the free layer ofNiFe was varied for the varying Ms×t. The film samples of Example 2 wereprepared by varying the thickness of the free layer of CoFe. All thesamples were thermally annealed at 270° C. for 10 hours in a magneticfield of 7 kOe, and their data were measured.

In Comparative Case 2 and Examples 1 and 2, the high-conductivity layeris of Cu, having a thickness of 2 nanometers. The points of Ms×t in thefree layer as indicated by the arrows in FIG. 16 are for the films (1)to (4) of Comparative Cases mentioned above. For the Ms×t in the freelayer in all samples, Ms of NiFe is 1T and Ms of CoFe is 1.8T. All thefree layer thickness are expressed in terms of thickness with Ms of 1Tesla.

In the films of Comparative Cases 1, 3 and 4 where no high-conductivitylayer is provided on the free layer, MR ratio is greatly lowered withthe reduction in Ms×t in the free layer. These films could hardly ensurehigh output capable of satisfying high-density recording.

In the film of Comparative Case 2 having a high-conductivity layer, thefree layer Ms×t dependence of the MR ratio is relatively small. However,since the antiferromagnetic layer in this film is of FeMn, notcontaining a noble metal, the thermal stability for MR ratio in thermaltreatment is low. With such small MR ratio, the film could not ensurehigh output for high-density recording.

In the films of Comparative Case 2 and Comparative Case 3, if a layer ofCo or CoFe having a thickness of 0.5 nanometers is inserted between thespacer of Cu and the free layer of NiFe, the MR ratio will increase by 1to 2% above the data in the graph of FIG. 16. Even if so, however, theMs×t dependence of the MR ratio is still the same as that in thesingle-layer NiFe free layer. Anyhow, small MR ratio will do well in theregion where Ms×t in the free layer is small.

On the other hand, in the films of the invention where ahigh-conductivity layer is provided adjacent to the free layer and theantiferromagnetic layer contains a noble metal, the thermal stabilityfor the MR ratio after thermal treatment is good. The films of theinvention produce high output well applicable to high-density recording.In particular, the difference in the MR ratio between the films of theinvention and those of Comparative Cases is obvious in the region whereMs×t is smaller than 5 nanometer Tesla.

The magnetoresistance effect device of the invention is described indetail hereunder.

FIG. 1 is a conceptual view showing the sectional constitution of themagnetoresistance effect device of the invention. As illustrated, themagnetoresistance effect device of the invention comprises ahigh-conductivity layer 101, a free layer 102, a spacer layer 103, afirst ferromagnetic layer 104, a coupling film 105, a secondferromagnetic layer 106 and an antiferromagnetic film 107, all laminatedin that order.

In the device with that constitution, the free layer 102 is muchthinned. On the transfer curve where Hs is small due to ultra thin freelayer, Hcu, Hpin and Hin are all small Hpin−Hin=Hcu, and a good biaspoint can be realized in the device. In general, in ultra-thin freelayers, high MR ratio is difficult to realize. The device of theinvention has overcome this problem. The device has good thermalstability for MR ratio, and therefore can realize high-output heads.

Specifically, even though having the ultra-thin free layer forhigh-density recording, the spin valve film constitution of theinvention can realize good bias point and can maintain high MR ratio.Therefore, the film stably produces high output. Concretely, in biaspoint designing, the condition of Hpin−Hin=Hcu is realized, and the filmhas good bias point. Reducing all Hpin, Hin and Hcu is important forstably realizing the condition of Hpin−Hin=Hcu.

Regarding Hpin, the film has a so-called Synthetic AF structure wherethe two ferromagnetic layers are antiferromagnetically coupled to eachother. In this, therefore, Hpin is derived from only the difference inthe magnetic thickness between the two layers of the first and secondferromagnetic layers, and can be reduced.

From the formula (1-4), it is understood that reducing (Ms×t)pin in thepinned layer is effective for reducing Hpin.

However, for bias point designing in ultra-thin free layers, only thereduction in Hpin is meaningless. For this, the reduction in the currentmagnetic field Hcu is indispensable. Therefore, the nonmagnetichigh-conductivity layer is provided on the free layer at the sideopposite to the side of the spacer layer, whereby the center of thecurrent distribution in the spin valve film can be near to the freelayer and Hcu can be thereby reduced. This is because, in the formulae(1-5) and (1-5-1), when I₃ is increased for the top-type spin valve film(I₁ is increased for the bottom-type spin valve film) and the currentflow ratio C is lowered, then the current magnetic field Hcu can bereduced. Another significant function of the nonmagnetichigh-conductivity layer is to maintain high MR ratio in the ultra-thinfree layer, to which the invention is directed, owing to the spin filtereffect. Specifically, by providing the nonmagnetic high-conductivitylayer, the difference in the mean free path of up-spin can be kept largebetween the parallel condition and the antiparallel condition for themagnetization directions of the free layer and the pinned layer adjacentto the spacer.

For stably realizing the condition of Hpin−Hin=Hcu, the reduction in Hinis also important. For realizing the high MR ratio owing to thehigh-conductivity layer as provided adjacent to the ultra-thin freelayer (spin filter effect), it is important to thin the spacer. However,in general, Hin will increase with the reduction in the spacer thicknessand with the reduction in the free layer thickness. Overcoming thisproblem, it is important to use the device of the invention at Hinfalling within a range of from 0 to 20 Oe or so.

FIG. 2 is a schematic view of the transfer curve given by the spin valvefilm of the invention. Even in the small transfer curve for which theultra-thin free layer is used to give small Hs, all of Hpin, Hcu and Hinare reduced, and it is possible to design the condition of Hpin−Hin=Hcu.Therefore, it is possible to settle the bias point in a good site ofaround 50% (good bias point around 40% in the value calculated by ourmethod). In addition, since the film incorporates the high-conductivitylayer exhibiting the spin filter effect, it still maintain high MR ratioeven in the ultra-thin free layer. The value in the vertical axis inFIG. 2 is satisfactorily high.

Next, the determinant factors for the bias point, namely the parametersof Hpin, Hin and Hcu are described in detail.

First, low Hcu is referred to. As previously described hereinabove, thehigh-conductivity layer is provided on the free layer at the sideopposite to the side of the spacer, whereby the value C in the formula(1-5) is reduced and the current magnetic field Hcu is reduced. Oneconcrete example of the film constitution is mentioned below.5 nanometer Ta/x nm Cu/2 nm CoFe/2 nm Cu/2.5 nm CoFe/0.9 nm Ru/2 nmCoFe/7 nm IrMn/5 nanometer Ta

FIG. 3 is a graph of the Cu thickness of the high-conductivity Cu layeradjacent to the free layer on the side opposite to the side at which thespacer is contacted with the free layer, versus the current magneticfield Hcu applied to the free layer. The sense current is 4 mA. Asillustrated, the value C of the formula (1-5) becomes small with theincrease in the Cu film thickness, whereby the current magnetic fieldHcu is reduced. When the current flow ratio in the upper and lower sidesof the free layer is the same, the current magnetic field applied to thefree layer is always zero irrespective of the intensity of the sensecurrent applied thereto.

One key point of the invention is to reduce the current magnetic field.However, it is undesirable to make the current magnetic field Hcu zero.The invention satisfies the condition of Hpin−Hin=Hcu for bias pointcontrol. Therefore, designing the current magnetic field to reach zero,as in the Comparative Case 3 mentioned above, will make the intendedbias point control impossible.

From the viewpoint of the current magnetic field, the suitable range ofthe nonmagnetic high-conductivity Cu layer may fall a broad scope offrom 0.5 nanometers to 4 nanometers. Since Hs is smaller with thereduction in the free layer thickness, it is desirable that the currentmagnetic field Hcu is smaller. In this Example, the nonmagnetichigh-conductivity layer is of Cu. Apart from this, when the layer is ofany other metal material or of a laminate film, it thickness could be interms of the thickness of the Cu layer. For example, where thenonmagnetic high-conductivity layer is a laminate film of 1.5 nm Ru/1 nmCu, the specific resistivity of Ru therein is 30 μΩcm and that of Cu is10 μΩcm, as measured through experiments. Therefore, the thickness ofthe laminate film will correspond to the Cu layer thickness of (1.5nm×10 μΩcm/30 μΩcm)+1 nm=1.5 nm.

In the same manner, for other metallic laminate films for thenonmagnetic high-conductivity layer, the current flow ratio could beobtained on the basis of the experimental data of specific resistivityof the constituent metals, 10 μΩcm for Cu, 30 μΩcm for Ru, 10 μΩcm forAu, 10 μΩcm for Ag, 20 μΩcm for Ir, 70 μΩcm for Re, 20 μΩcm for Rh, 40μΩcm for Pt, 40 μΩcm for Pd, 12 μΩcm for Al, and 30 μΩcm for Os. Wherethe nonmagnetic high-conductivity layer is of an alloy, its thicknesscould be also in terms of the Cu layer thickness, based on the specificresistance of the constituent elements as above, for which the specificresistance data may be proportionally partitioned according to theelemental composition.

As so mentioned hereinabove for the Comparative Cases, the specificresistance of the metals constituting the nonmagnetic high-conductivitylayer will vary depending on the material with which the layer iscontacted. However, the material to be contacted with the nonmagnetichigh-conductivity layer does not differ so much in different spin valvefilms. Therefore, the suitable range of the thickness of the nonmagnetichigh-conductivity layer could be determined on the basis of the data ofthe specific resistance of the metals constituting the layer.

As in the formula (1-5), Hcu depends on the current flow ratio of theupper and lower layers above and below the free layer. Therefore, forreducing Hcu, it is desirable that the thickness of the spacer layer aspositioned at the side opposite to the side of the nonmagnetichigh-conductivity layer is as small as possible. This meets therequirement for the spin filter effect on MR ratio, which will bementioned hereunder. Concretely, it is desirable that the spacer filmthickness falls between 1.5 nanometers and 2.5 nanometers or so.

The nonmagnetic high-conductivity layer also functions as the layerexhibiting the spin filter effect on MR ratio with the reduction in thecurrent magnetic field Hcu. For its effect, the suitable range of thethickness of the layer will be limited in some degree. For example,where conductive electrons that move from the pinned layer to the freelayer are taken into consideration, it is desirable that the mean freepath for the electrons is large, depending on the magnetizationdirection of the free layer as to whether it is parallel or antiparallelto the magnetization direction of the pinned layer. Therefore, it isdesirable that the spacer film is thinner, not depending on spin-up orspin-down. To avoid increasing Hin, the preferred range of the spacerthickness falls between 1.5 nanometers and 2.5 nanometers.

It is also desirable that the free layer thickness is larger than themean free path for down spin but is much smaller than that for up spin.For example, since the free mean path for down spin of NiFe is around1.1 nanometers, it is the best that the NiFe thickness falls between 1nanometers and 4.5 nanometers or so, and that the CoFe thickness fallsbetween 1 nanometers and 3 nanometers or so. The most preferred range ofthe high-conductivity layer thickness varies, depending on the pinnedlayer thickness, the spacer thickness and the free layer thickness. Withthe spacer layer thickness being smaller, and with the free layerthickness being smaller, the thickness of the high-conductivity layerfor MR ratio peak is larger. For example, where the thickness of thepinned layer of CoFe is 2.5 nanometers, that of the spacer of Cu is 2nanometers and that of the free layer of CoFe is 2 nanometers, thehigh-conductivity layer of Cu having a thickness of around 2 nanometersgives MR ratio peak. In experiences, when the total thickness of thefree layer and the nonmagnetic high-conductivity layer of Cu fallsbetween 4 and 5 nanometers or so, the high-conductivity layer gives MRratio peak. Therefore, it is desirable that the thickness of thenonmagnetic high-conductivity layer is defined around the range. Wherethe nonmagnetic high-conductivity layer is of Cu, being adjacent to thefree layer, the preferred range of the total thickness of the Cu layerand the free layer falls between 3 nanometers and 5.5 nanometers or soincluding the margin.

Next referred to is Hpin. For reducing Hpin, it is desirable that theeffective thickness of the pinned layer of CoFe with Bs being 1.8T is atmost around 2 nanometers (at most around 3.6 nanometers in terms ofNiFe), more preferably at most 1.7 nanometer (at most 3 nanometers interms of NiFe), and most preferably at most 1 nanometer (at most 1.8nanometers in terms of NiFe). For realizing the preferred condition, itis desirable that the pinned layer has a Synthetic AF structure. Forexample, the structure is composed of antiferromagneticfilm/ferromagnetic film 1/0.9 nm Ru/ferromagnetic film 2, in which theferromagnetic film 1 is antiferromagnetically coupled to theferromagnetic film 2. One of the two ferromagnetic layer, theferromagnetic film 1 as antiferromagnetically coupled to the other ismagnetically pinned in one direction by the antiferromagnetic film. Themagnetization directions of the ferromagnetic film 1 and theferromagnetic film 2 are opposite to each other, and the couplingmagnetic field between them is several kOe and is large. Therefore, asprimary approximation, it is considered that the difference between Ms×tof the ferromagnetic film 1 and that of the ferromagnetic film 2 wouldcontribute to the effective pinned layer stray magnetic field (U.S. Pat.No. 5,465,185).

For example, in the preferred constitution of IrMn/2 nm CoFe/0.9 nmRu/2.5 nm CoFe, the effective thickness of the pinned layer will be 2.5nanometers−2 nanometers=0.5 nanometers (the magnetic thickness will be0.9 nanometer Tesla) Reducing the effective pinned layer thickness, ifpossible, brings about the reduction in Hpin, as in the formula (1-4).When the pinned layer of low Mst is realized by normal pinned structure,it is able to obtain the good bias point without synthetic AF structure.

Next referred to is Hin. From the viewpoint of the bias point and thespin filter effect, it is desirable the thickness of the Cu layer as thespacer is as small as possible, as so mentioned hereinabove. Concretely,it is desirable that, with such a thin spacer film, Hin falls between 0and 20 Oe or so, more preferably between 5 and 15 Oe or so. In theinvention, one resolution for the film constitution not increasing Hineven when the spacer is thin is a two-layered underlayer constitution orthe like.

Next referred to is the thermal stability for MR ratio. When ultra-thinfree layers are employed, it is extremely difficult to maintain goodthermal stability for MR ratio in thermal treatment. Concretely, twomeasures may be taken for improving the thermal stability for MR ratioof spin valve films incorporating an ultra-thin free layer. One is toprovide a nonmagnetic high-conductivity layer of a certain level,adjacent to the free layer. Needless-to-say, the nonmagnetichigh-conductivity layer exhibits the spin filter effect. In addition, ithas been found that the layer further acts to improve the thermalstability for MR ratio. It has been found that, though not sosignificant when the thickness of the neighboring free layer is around4.5 nanometers, the total thickness of the free layer and thenonmagnetic high-conductivity layer must be indispensably at least 1nanometer when the free layer is thinned to be around 2 nanometers. Forexample, when the nonmagnetic high-conductivity layer thickness is 0nanometer, the MR ratio after thermal treatment (at 270° C. for 10hours) will reduce by about 50% in terms of the relative ratio based onthe MR ratio in the as-deposited condition. However, if the nonmagnetichigh-conductivity layer of around 1 nanometer in thickness is provided,the MR ratio reduction is decreased to fall between 0 and 30%.

Even the first measure being taken, the thermal deterioration in MRratio will still fluctuate. The second measure is to compensate forthis, for which the material for the antiferromagnetic film isspecifically defined. When the antiferromagnetic film is FeMn, thethermal deterioration is 30%. However, when it is IrMn, the thermaldeterioration could be reduced to 0 to 15%. The MR ratio in theas-deposited film in which is used antiferromagnetic PtMn could not bemeasured, but the MR ratio in the film after thermal treatment is equalto that in the as-deposited film with IrMn. Namely, the thermaldeterioration in MR ratio in the film with PtMn is almost 0%. Thethermal stability to MR ratio depends on the noble metal content of theantiferromagnetic film. It has been found that antiferromagnetic filmscontaining a noble metal, for example, those of IrMn, PtMn, PdPtMn orRuRhMn are especially preferred for the spin valve films of theinvention comprising an ultra-thin free layer.

Summarizing the above, FIG. 4 is a graph concretely showing the range ofthe pinned layer thickness and the nonmagnetic high-conductivity layerthickness in Synthetic AF for realizing asymmetry of from −10% to +10%,or that is, for realizing bias points of from 30% to 50% by oursimplified calculation method. The “asymmetry” is defined as(V1−V2)/(V1+V2), in which V1 indicates the peak value of thereproduction output in a positive signal field and V2 indicates the peakvalue of the reproduction output in a negative signal field. The“asymmetry of from −10% to +10%” corresponds to “(V1−V2)/(V1+V2) fallingbetween minus 0.1 and plus 0.1”.

For realizing Hpin−Hin=Hcu, Hcu must be lowered when Hpin is small. Inother words, as in the formulae (1-4) and (1-5), when the thickness ofthe upper and lower films of the pinned layer in Synthetic AF,(Ms×t)pin, is small, the thickness of the nonmagnetic high-conductivitylayer must be large; but, on the other hand, when (Ms×t)pin is large,the thickness of the nonmagnetic high-conductivity layer must be small.

Concretely, the spin valve film with Synthetic AF of the invention shallsatisfy the conditions of 0.5 nanometers≦tm(pin1)−tm(pin2)+t(HCL)≦4nanometers and t(HCL)≧0.5 nanometers, in which tm(pin1) indicates thethickness of the pined layer constituting Synthetic AF, tm(pin2)indicates the thickness of the another pinned layer constituting it, andt(HCL) indicates the thickness of the nonmagnetic high-conductivitylayer (in terms of the Cu layer having a specific resistance of 10μΩcm). The condition of 0.5 nanometers≦tm(pin1)−tm(pin2)+t(HCL) is forthe limit for the bias point of around 30%, or that is, for theasymmetry of +10%; and the condition oftm(pin1)−tm(pin2)+t(HCL)≦4nanometers is for the limit for the bias pointof around 50%, or that is, for the asymmetry of −10%.“tm(pin1)−tm(pin2)” indicates the magnetic thickness of the pinned layerin terms of NiFe with Ms of 1T. For example, in a Synthetic AF structureof PtMn/2 nm CoFe/0.9 nm Ru/2.5 nm CoFe, the pinned layer thickness is(2.5−2)×1.8T=0.9 nanometers. In the structure incorporating thesingle-layer pinned layer in the above-mentioned Comparative Cases, usedis Ms×t of the single-layer pinned layer.

t(HCL) indicates the thickness of the nonmagnetic high-conductivitylayer in terms of Cu. Where the nonmagnetic high-conductivity layer isof any others except Cu, its thickness could be determined in terms ofCu, based on the above-mentioned data of the specific resistance of theconstituent component.

The condition of t(HCL)≧0.5 nanometers is to define the lowermost limitof the thickness of the nonmagnetic high-conductivity layerindispensable for realizing high MR in the spin valve films in which thethickness of the free layer is smaller than 4.5 nanometers. Morepreferably, t(HCL)≦3 nanometers. This is because, when the thickness ofthe nonmagnetic high-conductivity layer is larger than 3 nanometers, ΔRswill lower. Also preferably, tm(pin1)−tm(pin2)≦3 nanometers. This isbecause, if the difference in the thickness between the upper and lowerfilms of the pinned layer in Synthetic AF is larger than 3 nanometers,the thermal stability for the pinned magnetization of the pinned layerwill lower.

In FIG. 4, plotted are the data of the Comparative Cases 1 to 4mentioned above and those of Example 1 to be mentioned in detailhereunder. In the Synthetic AF structure, where the magnetic thicknessof the pinned film adjacent to the spacer is larger than that of theother pinned film, the magnetic thickness of the pinned layer in thehorizontal axis is in the plus side in the graph of FIG. 4; and wherethe magnetic thickness of the pinned film adjacent to the spacer issmaller than that of the other pinned film, the magnetic thickness ofthe pinned layer in the horizontal axis is in the minus side. In theconventional pin layer constitution with no Synthetic AF, the magneticthickness of the pinned layer is all in the plus side.

As is known from FIG. 4, the films of the Comparative Cases are alloutside the preferred range, or that is, their bias points are not goodand their asymmetry is large; but those of the invention all within thepreferred range, or that is, their bias points are all good and theirasymmetry is small.

Examples of concrete film structures of the invention are mentionedbelow, in which the small Hpin in Synthetic AF is canceled by the smallHcu to realize Hpin−Hin=Hcu through specific bias point designing andthe difficulties in improving the thermal stability for MR ratio that ispeculiar to ultra-thin free layer-incorporated spin valve films areovercome.

EXAMPLE 1 Top SFSV (with Free Layer of NiFe/Co(Fe))

5 nanometer Ta/x nm Cu/2 nm NiFe/0.5 nm CoFe/2 nm Cu/(2+y) nm CoFe/0.9nm Ru/2 nm CoFe/7 nm IrMn/5 nanometer Ta  (7-1)

This is to exemplify a so-called top-type spin valve film in which anantiferromagnetic layer is above a free layer.

FIG. 5 is a conceptual view showing a typical film constitution of themagnetoresistance effect device of this Example. Precisely, the deviceillustrated comprises a high-conductivity layer 101 peculiar to theinvention, a free layer 102 and a spacer layer 103 all laminated on asubbing buffer layer 112 in that order, and comprises pinnedferromagnetic layers 104 and 106 as antiferromagnetically coupled toeach other via a layer 105, in which the layer 106 is pinned in onedirection by an antiferromagnetic layer 10. On the antiferromagneticlayer 107, formed is a cap layer 113. In the film structure of (7-1),the free layer 102 is of a laminate film composed of two layers 110 and111, and the nonmagnetic high-conductivity layer 101 is a single layerof Cu.

The film (7-1) has achieved both good MR and good bias point control,owing to the MR spin filter effect of the subbing Cu layer and to theeffect of the Synthetic AF structure to reduce Hpin. The bias point datafor the film, as calculated according to the method mentioned above, arein Table 5.

TABLE 5 Calculated Bias Point Data MR height x = 2 (a) y = 0.5, Hin = 20Oe 0.3 μm 37% 0.5 μm 31% 0.7 μm 25% (b) y = 0.8, Hin = 20 Oe 0.3 μm 46%0.5 μm 40% 0.7 μm 33% (c) y = 0.5, Hin = 10 Oe 0.3 μm 42% 0.5 μm 39% 0.7μm 36%

The subbing Cu layer has a thickness of 2 nanometers. In the structurewhere the underlayer is a simple, single-layered, high-conductivitylayer of Cu, Hin is 20 Oe and is relatively large. In that structure, itis known from the data of Table 5-(a) where the difference in thethickness between the upper and lower pinned layers in the Synthetic AFis 0.5 nanometers, that the bias points are shifted to the minus side insome degree from the good bias point of 40%. The film with thatstructure is well practicable. The data of Table 5-(b) are for the caseof y=0.8 nanometers (Hpin is increased in some degree). In the structureof this case, the bias point data are better than those in the structureof (a) in which the bias point data are shifted lower. The case of (c)in which Hin is lowered also gives good bias point data. Comparing thedata of (a), (b) and (c) in Table 5, it is obvious that Hin ispreferably as small as possible. This is because of the reduced MRheight dependence of the bias point. In the Synthetic AF structure, thesmaller thickness difference between the upper and lower pinned layersgives smaller Hpin, thereby resulting in smaller MR height dependence ofthe bias point. However, the difference of 0.3 nanometers between (a)and (b) could be negligible. Preferably, therefore, y=0 to 1 nanometer(Ms×t=0 to 1.8 nanometer Tesla in NiFe), more preferably, y=0 to 0.5nanometers (Ms×t=0 to 0.9 nanometer Tesla in NiFe). Within the preferredrange, the value y is easy to control for obtaining good bias points andfor improving other characteristics of the film including ESDresistance, etc.

The subbing Cu layer is for bias point control and for MR spin filtereffect. Increasing the subbing Cu thickness results in small Hcu, butalso results in ΔRs reduction. Preferably, therefore, the Cu thicknessfalls between 0.5 nanometers and 4 nanometers, more preferably between0.5 nanometers and 3 nanometers. The subbing Cu thickness enough for theMR spin filter effect depends on the constitution of the free layer.With the free layer being thin, the most preferred thickness of thesubbing Cu layer enough for the MR spin filter effect will shift to alarger value. In experiments, the peak of MR ratio appeared when thetotal thickness of the subbing Cu layer and the free layer fell between4 nanometers and 5 nanometers.

In the free layer constitution in (7-1) where the subbing Cu thicknessis from 0 to 1.5 nanometers, the MR increase owing to the spin filtereffect of the increased Cu thickness will cancel the Rs reduction to becaused by the increase in the Cu thickness, and ΔRs changes little. Inanother where the subbing Cu thickness is from 1.5 nanometers to 2nanometers, however, ΔRs will decrease by about 0.1 Ω; and in stillanother where the subbing Cu thickness is from 1.5 nanometers to 3nanometers, ΔRs will decrease by about 0.25 Ω. The ΔRs reduction shallbe nearly proportional to the output reduction, and is thereforeunfavorable. However, if thick subbing Cu is desired for bias pointcontrol, the subbing Cu thickness could be 3 nanometers in the freelayer constitution illustrated. In this case, since the current magneticfield per the unit current is small and since the spin valve filmresistance is lowered, the output reduction to be caused by the ΔRsreduction could be retarded by applying increased current. This isbecause the output is also proportional to the applied current. If ΔRshas decreased by 10% owing to the increase in the subbing Cu thickness,the calculated sense current of 4 mA maybe increased to 5 mA whereby theoutput will increase by 25%. In that manner, the output reduction causedby the ΔRs reduction could be well compensated for by the currentincrease.

For a thick free layer of 4 nm NiFe/0.5 nm CoFe, the subbing Cuthickness is preferably from 0.5 to 2 nanometers or so; but for a thinfree layer of 1 nm NiFe/0.5 nm CoFe, the subbing Cu thickness ispreferably from 1 to 4 nanometers or so. The thickness of the interlayerof CoFe may be varied within a range of from 0.3 to 1.5 nanometers. Inplace of CoFe, also employable is any of Co or other Co alloys. Where Cois used in place of CoFe, its thickness is preferably as small aspossible. This is because the Co single substance could not be softmagnetic by itself.

For example, when NiFe is 4 nanometers thick, then Co is preferably from0 to 1 nanometer thick; when NiFe is 2 nanometers thick, then Co ispreferably from 0 to 0.5 nanometers thick; and when NiFe is 1 nanometerthick, then Co is preferably from 0 to 0.3 nanometers thick. If theinterfacial diffusion from the subbing Cu is desired to be prevented, alayer of a material not forming a solid solution with Cu, for example,Co or CoFe could be put between the subbing Cu layer and the free layer.For example, the free layer may have a structure of 0.3 nm Co/2 nmNiFe/0.5 nm Co, or 0.5 nm CoFe/2 nm NiFe/0.5 nm CoFe.

In place of the ultra-thin, laminated films of magnetic layers, an alloyfree layer of NiFeCo may also be employed.

Ultra-thin free layers to which the invention is directed could hardlyrealize low magnetostriction. One reason for the difficulty is that themagnetostriction of NiFe becomes larger in positive when the thicknessof the NiFe layer is smaller. In order to overcome the problem, the NiFecomposition could be Ni₈₀Fe₂₀ (at. %) in an ordinary free layer of 8 nmNiFe/1 nm CoFe. However, in the free layer of the invention having amagnetic thickness of not larger than 4.5 nanometer Tesla, it isdesirable that the NiFe composition is an Ni-rich one over Ni₈₀Fe₂₀.Concretely, for the NiFe film having a thickness of 4 nanometers or so,desired is an Ni-rich composition over Ni₈₁Fe₁₉ (at. %); and for theNiFe film having a thickness of 3 nanometers or so, desired is anNi-rich composition over Ni_(81.5)Fe_(18.5) (at. %). It is desirablethat the uppermost limit of the Ni content of NiFe is not over Ni₉₀Fe₁₀(at. %).

As mentioned above, the subbing Cu layer is to attain two major objects.One is to reduce the current magnetic field Hcu for good bias pointcontrol even in ultra-thin free layers; and the other is to exhibit theMR spin filter effect without lowering the MR ratio even in ultra-thinfree layers.

From the viewpoint of bias point control, the factors y and x in thefilm (7-1) are determined in mutuality but not independently. Forexample, when y is smaller, then Hpin is also smaller. In this case, thecurrent magnetic field Hcu to cancel Hpin is preferably also smaller,and the value of x is preferably larger for the best results.

Concretely, one example of film thickness designing where thenonmagnetic high-conductivity layer is of Cu is as follows: When thepinned layer has 2 nanometer Tesla, the Cu layer thickness is from 0.5to 1.5 nm; when the pinned layer has 1.5 nanometer Tesla, the Cu layerthickness is from 1 to 2 nm; when the pinned layer has 1 nanometerTesla, the Cu layer thickness is from 1.5 to 2.5 nm; when the pinnedlayer has 0.5 nanometer Tesla, the Cu layer thickness is from 2 to 3 nm;and when the pinned layer has 0 nanometer Tesla, the Cu layer thicknessis from 2.5 to 3.5 nm.

Where the pinned layer is of Co or CoFe, its thickness shall bet=(Ms×t)pin/1.8T [nanometer]; and where the pinned layer is of NiFe, itsthickness shall be t=(Ms×t)pin/1T [nanometer].

In the example 1, thickness of the pinned layer disposed to the spacerlayer is larger than that of the another pinned layer, however it ispossible that the pinned layer disposed on the spacer layer is smallerthat that of the another pinned layer. In that case, the direction ofthe current flow is opposite to the before case. In another wards, thedirection of the Hpin and the Hcu should be always opposite to eachother.

In place of Cu, the spacer layer may be of any other element of Au orAg, or may be of an alloy comprising those elements. However, Cu is thebest. For realizing high MR and for reducing as much as possible thethickness of the shunt layer that is on the free layer at the sideopposite to the side of the underlayer to thereby reduce the currentmagnetic field, it is desirable that the spacer thickness is as small aspossible. However, if the spacer is too small, the ferromagneticcoupling between the pinned layer and the free layer will increase toenlarge Hin. Preferably, therefore, the spacer thickness falls between1.5 nanometers and 2.5 nanometers, more preferably between 1.8nanometers and 2.3 nanometers.

The subbing high-conductivity layer to fill the significant roles of thespin filter effect and the current magnetic field reduction is herein asingle layer of Cu. The layer may also be of a laminate film. In thetop-type spin valve film, the layer acts also as an fcc seed layer.Therefore, the material of the underlayer is preferably an fcc or hcpmetal material. Concretely, the layer may be an alloy layer of metals ofAu, Ag, Al, Zr, Ru, Rh, Re, Ir, Pt, etc.; or it may be of a laminatelayer of those metals. For only the MR spin filter effect and thecurrent magnetic field reduction, the simple Cu underlayer will besatisfactory. The alloy layer or the laminate film for the underlayerhas additional two effects; one for magnetostriction control inultra-thin free layers and the other for Hin control therein.Concretely, the following example is mentioned.5 nanometer Ta/1 nm Ru/1.5 nm Cu/2 nm NiFe/0.5 nm CoFe/2 nm Cu/2.5 nmCoFe/0.9 nm Ru/2 nm CoFe/7 nm IrMn/5 nanometer Ta  (7-2)

With the Ru underlayer of 1 nanometer thick, the film smoothness isimproved, and with the spacer of 2 nanometers thick, Ms×t of the freelayer could be 2.9 nanometer Tesla in terms of NiFe. Thus, even thoughthe free layer is an ultra-thin layer, it readily realizes low Hin ofaround 10 Oe. Such low Hin is desirable, as the MR height dependence ofthe bias point is reduced. In addition, it is also desirable, as capableof realizing good bias point control even in the absence of anycomplicated thickness difference between the upper and lower pinnedlayers in the Synthetic AF. In the illustrated case (7-2), the Ruthickness is 1 nanometer, but is preferably from 0.5 nanometers to 5nanometers, more preferably from 1 nanometers to 3 nanometers or so. Thepreferred thickness range could apply to other materials except Ru.

In the film (7-2), Hcu corresponds to the sum of the electrical shuntlayers of Ru and Cu. For example, for Ru, its specific resistance is 30μΩcm and is about 3 times that of Cu. From the viewpoint of Hcu, thefilm (7-2) shall be equivalent to a film having a Cu thickness of 1.8nanometers. However, from the viewpoint of MR, the resistance of Ru ishigh and shortens the mean free path for electrons. Therefore, if Ru isdirectly contacted with NiFe, the film structure could not almostexhibit a spin filter effect. Therefore, it is desirable that the layerto be contacted with the free layer is of a low-resistance material suchas Cu, Au, Ag of the like. For Ru, it is desirable that it is contactedwith the free layer via Cu, Au, Ag or the like in the form of atwo-layered film. This is one reason why the underlayer is of atwo-layered film.

In the illustrated case, the buffer layer of Ta is used. However, if thehigh conductance layer could exhibit the buffer effect by itself, the Talayer will be not needed. For example, when a Zr layer is used in placeof Ru, the Ta layer may be omitted.

For the buffer layer, any of Ti, Zr, W, Cu, Hf, Mo or their alloys maybe employed in place of Ta. The thickness of the buffer layer made ofany of them preferably falls between 1 nanometer and 7 nanometers, morepreferably 2 nanometers and 5 nanometers or so.

In the illustrated case, the AF film is of IrMn (Ir: 5 to 40 at. %). TheIrMn film thickness preferably falls between 3 nanometers and 13nanometers or so. The merits of IrMn are that, since the IrMn film couldexhibit good pinning capabilities even though thin, it is suitable tonarrow gap heads for high-density recording, and that, as containing thenoble metal, it could maintain high MR ratio even after thermaltreatment. The antiferromagnetic film of FeMn as in Comparative Case 2could not maintain high MR ratio after thermal treatment. The demerit ofthe antiferromagnetic film of FeMn is especially remarkable inultra-thin free layers such as those in the invention.

As the antiferromagnetic film, also employable is any of CrMn, NiMn andNiO. However, for realizing high MR ratio, AF films containing a noblemetal are preferred. For example, in place of Ir, employable is Pd, Rhor the like. As compared with FeMn and NiMn films, the noblemetal-containing AF films are more effective for improving MR ratio, andtherefore could maintain high MR ratio even after annealing thermaltreatment that is indispensable to heads. Still another preferredexample of the materials for AF films is PtMn of which the noble metalcontent is much higher.5 nanometer Ta/x nm Cu/2 nm NiFe/0.5 nm CoFe/2 nm Cu/2.5 nm CoFe/0.9 nmRu/2 nm CoFe/10 nm PtMn/5 nanometer Ta  (7-3)5 nanometer Ta/x nm Ru/y nm Cu/2 nm NiFe/0.5 nm CoFe/2 nm Cu/2.5 nmCoFe/0.9 nm Ru/2 nm CoFe/10 nm PtMn/5 nanometer Ta  (7-4)

Using PtMn (Pt: 40 to 65 at. %) is advantageous in that, since the noblemetal content of this is much higher than that of IrMn noted above, theMR degradation in annealing is much lower and therefore high MR ratiocould be realized to enlarge ΔRs, whereby the output could be increased.In the spin valve film having an ultra-thin free layer which can hardlyrealize good thermal stability for MR, most preferred for the bestthermal stability for MR is a combination of a subbing Cu layer with aspin filter effect and a layer of PtMn. In place of PtMn, alsoemployable is PdMn or PdPtMn (noble metal content: 40 to 65 at. %).

From the viewpoint of thermal stability for MR, it is desirable that thesubbing Cu layer has a thickness of at least 1 nanometer. This isbecause, if the thickness of the Cu layer is smaller than 1 nanometer,the thermal stability for MR will be poor. However, when the thicknessof the NiFe layer is not smaller than 4 nanometers, the Cu layer maywell be 0.5 nanometers thick for good thermal stability for MR.

The specific electric resistance of PtMn is large and is nearly the sameas that of IrMn. Therefore, PtMn is favorable, as having littleinfluence on the current magnetic field. For those reasons, the films(7-3) ad (7-4) are extremely favorable to practical applications.

However, one demerit of PtMn is that, since its critical thickness forproducing a unidirectional anisotropic magnetic field is larger than thecritical thickness of IrMn, it is difficult to thin the PtMn film to 5nanometers or so. Therefore, when PtMn is used, it is desirable that thethickness of its film falls between 5 nanometers and 30 nanometers, morepreferably between 7 nanometers and 15 nanometers or so. The same ideaas in (7-4) where the underlayer below the free layer has a two-layeredstructure could apply also to PtMn.

As variations of the embodiments (7-1) to (7-4), a noble metal elementfilm could be laminated on the antiferromagnetic film. For example, asingle-layered or laminated film of any of Cu, Ru, Pt, Au, Ag, Re, Rh,Pd and the like may be used. The variations could realize low Hin evenwhen the spacer is thin. However, if the noble metal film is too thick,the current flow ratio will increase in the upper layers over the freelayer. Therefore, the thickness of the single-layered or laminated filmpreferably falls between 0.5 nanometers and 3 nanometers or so.

As has been mentioned hereinabove with reference to FIG. 15, the biaspoint control in the spin valve films of this Example is much betterthan that in those of Comparative Cases 1 to 4, and the films of thisExample could ensure the best bias points.

As also mentioned with reference to FIG. 16, the spin valve films ofthis Example produce higher MR ratio than that to be produced by thefilms of Comparative Cases 1 to 4 essentially bellow 45 nanometer Teslafree layer.

EXAMPLE 2 Top SFSV (with Simple CoFe Free Layer)

5 nanometer Ta/x nm Cu/2 nm CoFe/2 nm Cu/2.5 nm CoFe/0.9 nm Ru/2 nmCoFe/7 nm IrMn/5 nanometer Ta  (8-1)5 nanometer Ta/x nm Cu/2 nm CoFe/2 nm Cu/2.5 nm CoFe/0.9 nm Ru/2 nmCoFe/10 nm PtMn/5 nanometer Ta  (8-2)

In this Example 2, used is a simple free layer of a single-layer CoFe,being different from the laminate free layer of NiFe/Co or NiFe/CoFe asin Example 1. In FIG. 1, the structure of this Example 1 has asingle-layer CoFe as the free layer 102 and a single-layer Cu as thehigh-conductivity layer 101.

As already mentioned ultra-thin free layers below 4.5 nanometer Tesla inNiFe face various difficulties. The single-layer CoFe free layer isadvantageous in that the soft magnetic characteristics control isrelatively easy even though the thickness of the layer is extremelysmall. A third additive element of B, Cu, Al, Rh, Pd, Ag, Ir, Au, Pt,Ru, Re, Os or the like could be added to CoFe, if desired. However, ifpure Co is used in place of such CoFe alloys, soft magneticcharacteristics characteristics could not be realized. CoFe preferablyfalls between Co₈₅Fe₁₅ (at. %) and Co₉₆Fe₄ (at. %). As will be mentionedhereunder, the defined composition range for CoFe is based on themagnetostriction control.

From the view point of soft magnetic characteristics, the CoFe freelayer is preferably oriented in fcc(111). From the viewpoint of betterspin filter effect, the layer is preferably oriented in fcc(111) so asto reduce the resistance. However, a microcrystalline or amorphous freelayer of CoFeB is also employable.

Ms of the simple CoFe free layer is larger than that of NiFe. Therefore,for realizing the same degree of Ms×t, the CoFe layer could be thinnerthan the NiFe layer. From the viewpoint of the spin filter effect, thesimple CoFe free layer is preferred. For example, for realizing a freelayer of 4.5 nanometer Tesla, NiFe/CoFe must be 3.6 nm NiFe/0.5 nm CoFe,and its total thickness is about 4 nanometers. As opposed to this, thethickness of the simple CoFe free layer could be 2.5 nanometers. Thelatter is thinner by about 1.5 nanometers than the former, NiFe/CoFe.Where a high-conductivity layer is provided below the free layer of thetwo films, the down spin electrons will be filtered out, since they arethick as compared with the mean free path for down spin of about 1nanometer. However, at a total thickness of around 4 nanometers ofNiFe/CoFe, the mean free path for down spin will be near to that for upspin. In that condition, the underlying high-conductivity layer willproduce a simple shunt effect. Therefore, increasing thehigh-conductivity layer thickness causes MR reduction owing to the shunteffect.

On the other hand, for the simple CoFe, the mean free path of up spin islonger than 2.5 nanometers. Therefore, providing a high-conductivitylayer of which the thickness is not so large will results in theincrease in the mean free path for up spin, thereby increasing MR. Inexperiences and through experiments, it is known that, where Cu is usedfor the high-conductivity layer, MR peaks appear when the totalthickness of the Cu layer and the free layer of NiFe/CoFe or CoFe is 4nanometers or so, or falls between 3 nanometers and 5 nanometers. Inother words, when the high-conductivity layer that is necessary for biaspoint designing is relatively thick, NiFe/CoFe rather causes MRreduction owing to the shunt effect but not to the spin filter effect,while, on the other hand, CoFe satisfies both good bias point controland MR increase owing to the spin filter effect. Therefore, CoFe isadvantageous. This is because, as so mentioned hereinabove, the MR peaksdepend on the total thickness of the high-conductivity layer and thefree layer. Therefore, when the CoFe layer thickness is smaller, thenthe Cu layer thickness to give MR peaks shall be larger, and the spinfilter effect and the bias point control both could be augmented. Forthe reasons mentioned above, the simple CoFe free layer is preferred forspin valve films.

The thermal stability for MR of the laminated NiFe/CoFe free layer isworse than that of the simple CoFe free layer, and the simple CoFe freelayer is better, as producing large MR.

The simple CoFe free layer is still better than the ultra-thin,laminated NiFe/CoFe layer, as its magnetostriction control is easy. Inparticular, the interfacial magnetostriction is important in ultra-thinfree layers. Therefore, NiFe/CoFe is inferior to simple CoFe, as theformer shall have one additional interface.

The bias point in the constitution of (8-1) could fall within a goodrange of from 30 to 50% or so, as in Example 1. Also like in Example 1,the MR height dependence of the free layer in (8-1) is small.

Regarding the Ms×t dependence of the free layer, smaller Ms×t givessmaller saturation magnetization Hs on the transfer curve, and requiresseverer bias point control. Concretely, much reducing the currentmagnetic field is important, and increasing the high-conductivity layerthickness is needed. As previously mentioned hereinabove, in the spinvalve films of the invention, the thickness of the high-conductivitylayer capable of producing MR peaks owing to the spin filter effectshall be larger with the reduction in the thickness of the free layer.This well matches with the constitution of this Example. It isunderstood that the idea of designing the spin valve films of theinvention is favorable to heads for high-density recording.

Concretely, when Ms×t of the free layer is 4.5 nanometer Tesla and thethickness of the CoFe film is 2.5 nanometers, then the preferred rangeof the high-conductivity film thickness falls between 0.5 nanometers and4 nanometers or so, more preferably between 0.5 nanometer and 3nanometers or so in terms of the 10 microohm centimeter Cu; when Ms×t ofthe free layer is 3.6 nanometer Tesla and the thickness of the CoFe filmis 2 nanometers, then the preferred range of the high-conductivity filmthickness falls between 0.5 nanometer and 4 nanometers or so, morepreferably between 1 nanometers and 3.5 nanometers or so in terms of Cu;when Ms×t of the free layer is 2.7 nanometer Tesla and the thickness ofthe CoFe film is 1.5 nanometers, then the preferred range of thehigh-conductivity film thickness falls between 0.5 nanometers and 4nanometers or so, more preferably between 2 nanometers and 4.5nanometers or so in terms of Cu; and when Ms×t of the free layer is 1.8nanometer Tesla and the thickness of the CoFe film is 1 nanometer, thenthe preferred range of the high-conductivity film thickness fallsbetween 0.5 nanometers and 4 nanometers or so, more preferably between 2nanometers and 4 nanometers or so in terms of Cu.

In (8-1) IrMn is used as the antiferromagnetic film; while in (8-2),PtMn is used as the same. Using PtMn is more advantageous in that thethermal stability for MR is much more improved and the output is muchmore increased. This is the same as in the case of the NiFe/Co(Fe) freelayer. However, PtMn is problematic in that Hin will readily increase.Therefore, for good bias point control, either the measure of morereducing the current magnetic field Hcu or the measure of moreincreasing Hpin will be needed for PtMn than for IrMn. For reducing Hcu,σt in the high-conductivity layer may be increased, or that is, thethickness of the high-conductivity layer may be increased. Because oflarge Hin, the difference in the thickness between the upper and lowerpinned layer in the Synthetic AF may be increased more for PtMn than forIrMn. However, increasing the thickness of the high-conductivity layerwill cause the reduction in ΔRs. Therefore, as compared with that forIrMn, it is desirable that the thickness of the high-conductivity layermay be controlled to fall between 0.5 and 3 nanometers or so in terms ofCu for PtMn. As previously mentioned herein, increasing Δt in theSynthetic AF structure is unfavorable since it increases the MR heightdependence of the bias point. Therefore, as compared with that for IrMn,it is desirable that the intrinsic thickness of the pinned layer may beincreased by from 0 to 1 nanometer or so in terms of CoFe for PtMn. Thefollowing variations of (8-1) and (8-2) are within the scope of theinvention.5 nanometer Ta/x nm Ru/y nm Cu/2 nm CoFe/2 nm Cu/2.5 nm CoFe/0.9 nm Ru/2nm CoFe/7 nm IrMn/5 nanometer Ta  (8-3)5 nanometer Ta/x nm Ru/y nm Cu/2 nm CoFe/2 nm Cu/2.5 nm CoFe/0.9 nm Ru/2nm CoFe/10 nm PtMn/5 nanometer Ta  (8-4)

In those variations, the high-conductivity layer is of a laminate filmof Ru/Cu but not a single-layer Cu. The reasons for the laminate filmare the following two.

1. CoFe magnetostriction control.

2. Hin reduction.

The CoFe magnetostriction control of 1 is to control themagnetostriction of CoFe through the distortion control of itself, aswill be mentioned hereunder. Specifically, the fcc-d(111) spacing inCoFe is enlarged more than the that on simple Cu, high conductivitylayer magnetostriction in the CoFe free layer is controlled to be nearlyzero. The magnetostriction of Co₉₀Fe₁₀ (at. %) is often enlarged in thenegative side in an ordinary condition. Therefore, the material to bebelow the Cu layer preferably has a large atomic radius than Cu. Forexample, Ru is preferred. In addition to this, also preferred are Re,Au, Ag, Al, Pt, Rh, Ir, Pd, etc. For the magnetostriction control, theunderlayer is made to have a two-layered structure, or the CoFecomposition may be varied from 90-10 at. % to any others. Concretely,employable are CoFe alloy free layers having a varying composition offrom Co₉₀Fe₁₀ to Co₉₆Fe₄.

The Hin reduction of 2 is because Ru has the ability to planarize thegrowing film. As previously mentioned hereinabove, Hin is preferably assmall as possible for good bias point designing based on Hcu and Hpin.In particular, the spacer thickness is preferably as small as possiblein two points of the MR spin filter effect and the shunt reduction inthe upper free layer. For this, needed is a technique of using anultra-thin spacer of Cu having a low Hin. In the constitution having alaminate Ru/Cu film, where the underlayer is of 1.5 nm Ru/1 to 2 nm Cu,the free layer of CoFe is an ultra-thin free layer having Ms×t of 3.6 nmand a thickness of 2 nanometers, and the spacer Cu has a thickness of 2nanometers, Hin could be from 7 to 13 Oe or is low. Considering the factthat Hin in the embodiments of (7-1) and (7-2) is around 20 Oe, the Hinreduction in the embodiments (8-3) and (8-4) is significant.

For Hcu calculation, σt shall be obtained from the specific resistanceof Ru in terms of Cu having 10 microohm centimeter. The specificresistance of Ru as obtained in experiments is 30 μΩcm. For the shunteffect, the thickness of Ru could be ⅓ of that of Cu having a specificresistance of 10 μΩcm. For example, the shunt in the constitution of 1.5nm Ru/1 nm Cu could be equivalent to that in Cu of (1.5 nanometers/3)+1nanometer=1.5 nanometer in thickness.

In variations of the embodiments (8-1) to (8-4), a noble metal elementfilm may be further laminated over the antiferromagnetic film. Forexample, employable is any of a single-layered or laminated films of Cu,Ru, Pt, Au, Ag, Re, Rh, Pd, etc. In those constitutions, low Hin couldbe realized even when the spacer film therein is thin. However, if thelaminated film is too thin, the current flow ratio will be large in theupper free layer. Therefore, the thickness of the single-layered orlaminated film preferably falls between 0.5 nanometers and 3 nanometersor so.

EXAMPLE 3 Bottom SFSV (with NiFe/Co(Fe) Free Layer)

5 nanometer Ta/2 nm Ru/10 nm PtMn/2 nm CoFe/0.9 rim Ru/2.5 nm CoFe/2 nmCu/0.5 nm Co/2 nm NiFe/2 nm Cu/5 nanometer Ta  (9-1)5 nanometer Ta/1 nm Ru/2 nm NiFeCr/7 nm IrMn/2 nm CoFe/0.9 nm Ru/2.5 nmCoFe/2 nm Cu/0.5 nm Co/2 nm NiFe/2 nm Cu/5 nanometer Ta  (9-2)

This is to exemplify a so-called bottom-type spin valve film in which anantiferromagnetic layer is below a free layer. FIG. 6 is a conceptualview showing the spin valve film constitution of this Example.Precisely, the film illustrated comprises an antiferromagnetic filmcrystallization control layer 128 and an antiferromagnetic film 127 aslaminated on a subbing buffer layer 131, and comprises pinned layers 126and 124 as antiferromagnetically coupled to each other via a layer 125.On the layer 124, laminated are a spacer layer 123, a free layer 122 anda nonmagnetic high-conductivity layer 121 in that order. Finallyprovided is a cap layer 132 over them.

In the embodiment of (9-1), the antiferromagnetic film crystallizationcontrol layer 128 is a single layer of Ru, the antiferromagnetic film127 is of PtMn, and the free layer 122 is of a laminate film composed oftwo layers 129 and 130. In the embodiment of (9-2), theantiferromagnetic film crystallization control layer 128 is atwo-layered film composed of a film 133 of Ru and a film 134 of NiFeCr,the antiferromagnetic film 127 is of IrMn, and the free layer 122 is ofa two-layered film composed of two layers 129 and 130.

In the bottom-type spin valve film, the antiferromagnetic filmcrystallization control layer is provided over the buffer layer of Ta orthe like, and it is a subbing film of fcc or hcp having a thickness offrom 1 nanometer to 5 nanometers or so. For example, employed are alloyfilms or laminate films of Cu, Au, Ru, Pt, Rh, Ag, Ni, NiFe, etc. Theseed layer is important for increasing the function of theantiferromagnetic film. In the embodiment of (9-1) incorporating PtMn,used is a single-layered Ru layer; while in (9-2) incorporating IrMn,used is a laminate film of Ru/NiFeCr. In the constitution with theantiferromagnetic film crystallization control layer of that type, theblocking temperature for the antiferromagnetic film could be elevated toa satisfactorily high level, the film planarization could be promoted,and low Hin could be realized even for the ultra-thin spacers of from1.5 to 2.5 nanometers thick or so that are needed in the invention.

The bias point control to be effected in the invention is not so muchinfluenced by the type of the seed layer when the thickness of the seedlayer falls within the range defined in this Example. However, lowresistance materials having a small specific resistance are unfavorableto the seed layer. This is because, if the shunt current flow isincreased in the layer, it would be difficult to make the current centernear to the free layer. Therefore, for the seed layer, it is desirableto use materials having as high as possible resistance and capable ofenhancing the function of the antiferromagnetic film. For example, inplace of using low-resistance NiFe alone, any of Cr, N, Hf, W, Ta andthe like may be added to NiFe so as to increase the specific resistanceof the NiFe layer. In (9-2), used is NiFeCr in place of NiFe.

As the antiferromagnetic film, used is PtMn in (9-1), and IrMn in (9-2).PtMn is advantageous in that the blocking temperature is high, thatHu.a. is large, and that the thermal stability for MR is lowered littleafter thermal treatment. With PtMn being used, therefore, high MR andhigh ΔRs could be realized. Like in the top-type structure, the merit ofthe noble metal-containing antiferromagnetic film of PtMn in thebottom-type structure is significant in that high MR could be maintainedstill after thermal treatment and even when ultra-thin free layers areused. In place of PtMn, PdPtMn is also employable. The preferredthickness range of the layer falls between 5 nanometers and 30nanometers, more preferably between 7 nanometers and 15 nanometers.

The merit of IrMn in (9-2) is that it can maintain its characteristicseven when its thickness is smaller than the thickness of PtMn.Therefore, IrMn is suitable to narrow-gap heads for high-densityrecording. Preferably, the IrMn thickness falls between 3 nanometers and13 nanometers. The IrMn film is also an antiferromagnetic filmcontaining the noble metal Ir, and its thermal stability for good MRratio is excellent. In place of IrMn, also employable is noblemetal-containing RuRhMn.

As mentioned above, PtMn, IrMn and PdPtMn are the best for theantiferromagnetic film. However, the bias point control in the spinvalve films of the invention is not limited by the material of theantiferromagnetic film. In the invention, also employable are any otherantiferromagnetic films of NiO, CrMnPt, NiMn, α-Fe₂O₃, etc.

As the ferromagnetic material for the two pinned layer in the SyntheticAF structure, herein used is an CoFe alloy. In place of this, alsoemployable are Co, NiFe and even laminate films of NiFe with Co or CoFe.Regarding the constituent materials and the film thicknesses, the sameas in the top-type structures of Examples 1 and 2 noted above couldapply to the bottom-type structure herein. The most significant objectof the Synthetic pinned layer structure, which is the key point in theinvention, is to reduce the pinned stray magnetic filed, as so mentionedhereinabove. The difference in Ms×t between the upper and lowerferromagnetic layers shall be closely related to the thickness of thehigh-conductivity layer as provided adjacent to the free layer.

Regarding the spacer, the same idea as that for the top-type structureshall apply also to the bottom-type structure. Also in the bottom-typestructure, the spacer layer is as thin as possible. Concretely, thespacer thickness preferably falls between 1.5 nanometers and 2.5nanometers, more preferably between 1.8 nanometers and 2.3 nanometers.

In this Example, the free layer is of a laminate film of NiFe/Co.Regarding the thickness and the material of the free layer, the same asin the top-type structure shall apply to the bottom-type structure.However, the NiFe composition for the subbing film differs between thetop-type structure and the bottom-type structure, and the preferred NiFecomposition for realizing low magnetostriction in the bottom-typestructure differs in some degree from that in the top-type structure.Concretely, in the case of a laminated free layer of NiFe/CoFe, thepositive side shifting of the magnetostriction in the laminatedNiFe/CoFe free layer to be caused by the reduction in the thickness ofNiFe in the bottom-type structure is smaller than that in the top-typestructure. Therefore, in the bottom-type structure, Ni-poorer NiFecompositions could well realize the reduction in the magnetostrictionthan in the top-type structure.

For example, in the case of a laminated free layer of 3 nm NiFe/0.5 nmCoFe, the NiFe composition of Ni₈₁Fe₁₉ (at. %) is not applicable to thetop-type structure as the magnetostriction in the positive side islarge, but is applicable to the bottom-type structure as themagnetostriction in the positive side is satisfactorily small inpractical applications.

The high-conductivity layer is the second significant key point in theinvention the same as the top type spin valve as mentioned before. Inthis Example, the high-conductivity layer is of a Cu film. The mostsignificant role of the high-conductivity film is to make the currentcenter near the free layer as much as possible thereby reduce thecurrent magnetic field.

Still another role of the film is to exhibit the spin filter effect forMR owing to the conductivity of Cu. Therefore, even through theultra-thin free layer is employed herein, the MR ratio degradation issmall.

Regarding the optimum thickness range of the Cu layer, the same as ininvention of the top type spin-valve may apply also to the bottomspin-valve of this Example. Like in the top-type structure, the optimumthickness range of the Cu layer varies also in bottom-type structure,depending on the thickness of the free layer, and on the difference inthe thickness between the upper and lower pinned layers of the SyntheticAF. In addition to its role for bias point control and for high MR ratioretention, still another important role of the Cu cap layer is torealize low Hin in ultra-thin free layers. For example, when Hin in afree layer is 30 Oe or more in the absence of the Cu cap layer, it couldbe reduced to about 10 Oe in the same free layer in the presence of theCu cap layer.

In variations of (9-1) and (9-2), the high-conductivity layer may be ofa laminate film composed of at least two layers, in place of thesingle-layer high-conductivity layer of Cu as disposed adjacent to thefree layer of CoFe. For example, the laminate film for thehigh-conductivity layer may include Cu/Ru, Cu/Re, Cu/Rh, Cu/Pt, etc. Theessential object of the two-layered high-conductivity layer is tocontrol the magnetostriction λs in the free layer. This is because, asso mentioned hereinabove for the top-type structure, themagnetostriction in the free layer of CoFe is influenced by thedistortion of the free layer itself. Moreover reduction in Hin isimportant in the invention. For reducing Hin, the two-layeredhigh-conductivity layer will be effective.

Embodiments of the variations are mentioned below.5 nanometer Ta/2 nm Ru/10 nm PtMn/2 nm CoFe/0.9 nm Ru/2.5 nm CoFe/2 nmCu/0.5 nm Co/2 nm NiFe/1.5 nm Cu/1.5 nm Ru/5 nanometer Ta  (9-3)5 nanometer Ta/1 nm Ru/1 nm NiFeCr/7 nm IrMn/2 nm CoFe/0.9 nm Ru/2.5 nmCoFe/2 nm Cu/0.5 nm Co/2 rim NiFe/1.5 nm Cu/1.5 nm Ru/5 nanometerTa  (9-4)

In those film structures, the specific resistance of Ru is 30 μΩcm whilethat of Cu is 10 μΩcm. For the electrical shunt effect, Cu of 1nanometer Thick will be equivalent to Ru of 3 nanometer Thick. In otherwords, in the films (9-3) and (9-4), the thickness of thehigh-conductivity film is equivalent to 2 nanometers in terms of Cu. Forthe single-layer Cu, its thickness may fall between 0.5 nanometers and 4nanometers. Therefore, for Ru, its thickness may fall between 0.5nanometers and 12 nanometers. However, Ru has a higher specificresistance than Cu and its spin filter effect is much lower than that ofCu. Therefore, for the high-conductivity layer to be adjacent to CoFe,Cu is preferred to Ru. Too thick Ru is unfavorable, as not satisfyingnarrow gaps. For these reasons, therefore, it is desirable that Cu ispositioned adjacent to CoFe, while having a thickness of from 0.5 to 2nanometers or so, and the other additional metal layer is positionedover the Cu layer to give the laminated film for the high-conductivitylayer.

EXAMPLE 4 Bottom SFSV (with Free CoFe Layer)

5 nanometer Ta/2 nm Ru/10 nm PtMn/2 nm CoFe/0.9 nm Ru/2.5 nm CoFe/2 nmCu/2 nm CoFe/2 nm Cu/5 nanometer Ta  (10-1)5 nanometer Ta/1 nm Ru/2 nm NiFeCr/7 nm IrMn/2 nm CoFe/0.9 nm Ru/2.5 nmCoFe/2 nm Cu/2 nm CoFe/2 nm Cu/5 nanometer Ta  (10-2)

This is to exemplify other embodiments of the bottom-type structure ofFIG. 6, in which the free layer 122 is of a single-layered CoFe. Theothers are the same as in Example 3. The materials of the other layersexcept the free layer and the thicknesses of those other layers are thesame as in Example 3. The merits of the single-layered free layer ofCoFe are the same as in the top-type structure. In this Example, Ms×t is3.6 nanometer Tesla in terms of NiFe. When this is compared with Ms×t of4.5 nanometer Tesla, the thickness of the single CoFe free layer couldbe 2.5 nanometers and is thin. Even so thin, the single CoFe free layercould enjoy good spin filter effect. However, the two-layered free layerof NiFe/Co(Fe) shall have a large thickness to be 4 nm NiFe/0.5 nm Co,and it could not enjoy the spin filter effect for MR but shall be asimple shunt layer. In addition, NiFe itself also exhibits the shunteffect. Therefore, ΔRs in the two-layered free layer is reduced by 0 to30%, based on that in the single-layered CoFe free layer.

As in the above, since the single-layered CoFe free layer in thisExample could enjoy the MR spin filter effect in a broad range of Ms×t,it is better than the laminated free layer in Example 3.

In variations of (10-1) and (10-2), the high-conductivity layer may beof a laminate film composed of at least two layers, in place of thesingle-layer high-conductivity layer of Cu as disposed adjacent to thefree layer of CoFe. For example, the laminate film for thehigh-conductivity layer may include Cu/Ru, Cu/Re, Cu/Rh, etc. Theessential object of the two-layered high-conductivity layer is tocontrol the magnetostriction λs in the free layer. This is because, asso mentioned hereinabove, the magnetostriction in the free layer of CoFeis influenced by the distortion of the free layer itself. Reduction inHin is important in the invention. For reducing Hin, the two-layeredhigh-conductivity layer will be effective. Embodiments of the variationsare mentioned below.5 nanometer Ta/2 nm NiFe/10 nm PtMn/2 nm CoFe/0.9 nm Ru/2.5 nm CoFe/2 nmCu/2 nm CoFe/1.5 nm Cu/1.5 nm Ru/5 nanometer Ta  (10-3)5 nanometer Ta/2 nm NiFe/7 nm IrMn/2 nm CoFe/0.9 nm Ru/2.5 nm CoFe/2 nmCu/2 nm CoFe/1.5 nm Cu/1.5 nm Ru/5 nanometer Ta  (10-4)

In place of controlling the magnetostriction in CoFe by means of thelaminated film for the nonmagnetic high-conductivity film as in theabove, the magnetostriction in the free layer could also be controlledby varying the composition of CoFe for the free layer. In general, it iseasy to modify the subbing film for distortion control in the freelayer. However, in bottom-type structures, it is often difficult tofreely select the material for the subbing film for the free layer. Inbottom-type structures, CoFe is laminated on Cu. In those, if Co₉₀Fe₁₀(at. %) is employed, the magnetostriction of the free layer in thenegative side will increase. In order to correct the magnetostriction tothe positive side, Co-rich CoFe is desired. Concretely, desired are CoFefree layers of Co₉₀Fe₁₀ (at. %) to Co₉₆Fe₄ (at. %). However, the Cocontent of the free layer is too large, the Co-rich composition willhave an hcp phase whereby the soft magnetic characteristics of the freelayer will be lowered (that is, Hc in the free layer is increased).Therefore, too Co-rich CoFe alloys such as Co₉₈Fe₂ are unfavorable.

In those film structures, the specific resistance of Ru is 30 μΩcm whilethat of Cu is 10 μΩcm. For the electrical shunt effect, Cu of 1nanometer Thick will be equivalent to Ru of 3 nanometer Thick. In otherwords, in the films (10-3) and (10-4), the thickness of thehigh-conductivity film is equivalent to 2 nanometers in terms of Cu. Forthe single-layer Cu, its thickness may fall between 0.5 nanometers and 4nanometers. Therefore, for Ru, its thickness may fall between 0.5nanometers and 12 nanometers. However, Ru has a higher specificresistance than Cu and its spin filter effect is lower than that of Cu.Therefore, for the high-conductivity layer to be adjacent to CoFe, Cu ispreferred to Ru. Too thick Ru is unfavorable, as not satisfying narrowgaps. For these reasons, therefore, it is desirable that Cu ispositioned adjacent to CoFe, while having a thickness of from 0.5 to 1nanometer or so, and the other additional metal layer is positioned overthe Cu layer to give the laminated film for the high-conductivity layer.

Second to Sixth Embodiments: Improvement in High-Temperature Stabilityand Reproduction Output Power

The second to sixth embodiments of the invention are mentioned below,which are directed to the improvement in the high-temperature stabilityand the reproduction output power.

First mentioned is the outline of the technical idea common to thesecond to sixth embodiments.

FIG. 17 shows one example of the second to sixth embodiments of theinvention. In FIG. 17, a lower shield 11 and a lower gap film 12 areprovided on a substrate 10, and a spin valve device 13 is providedthereon. The spin valve device comprises a spin valve film 14 and a pairof longitudinal bias films 15 and a pair of electrodes 16. The spinvalve film 14 comprises nonmagnetic underlayers 141, 142, anantiferromagnetic layer 143, a pinned magnetic layer 144, an interlayer145, a free layer 146 and a protective film 147.

Table 6 shows the material composition of the antiferromagnetic layer tobe coupled with the ferromagnetic layer in SyAF which is the pinnedmagnetic layer of the invention, the thickness of the antiferromagneticlayer, the magnetic coupling coefficient J at 200° C., the magneticcoupling bias field H_(UA)* or H_(UA) at 200° C., the blockingtemperature Tb, and the resistance change rate ΔR/R in the spin valvedevice. Table 7 shows the same data as in Table 6, but in Table 7, thepinned magnetic layer is a conventional, single-layered, pinned magneticlayer. Table 8 shows the half-value width of the diffraction peak fromthe close-packed plane of the antiferromagnetic layer as coupled to SyAFin its rocking curve, Δθ; the magnetic coupling coefficient J at 200° C.to the ferromagnetic layer adjacent to the antiferromagnetic layer inSyAF; and the blocking temperature Tb.

TABLE 6 Spin Valve Film Constitution: Substrate/5 nanometerTa/NiFe/CoFe/3 nm Cu/2.5 nm CoFe/0.9 nm Ru/2.5 nm CoFe/antiferromagneticlayer/5 nanometer Ta Antiferromagnetic Layer Blocking Resistance Thick-J H_(UA)* Temperature Change ness (erg/cm²) (Oe) Tb Rate ΔR/R Material(nm) at 200° C. at 200° C. (° C.) (%) Ir22Mn78 5 0.04 400 250 7.3 (comp.7 0.045 450 270 7.3 case) 1 0.045 450 290 7 20 0.04 400 300 6.5 30 0.035350 300 5.5 Rh20Mn80 7 0.025 250 235 7.1 10 0.035 350 260 6.8 Rh14Ru7M 70.02 200 225 7.2 n79 10 0.03 300 245 6.8 Pt53Mn47 10 0.02 250 290 7.9(comp. 15 0.025 400 320 7.4 case) 20 0.1 >600 350 7 30 0.12 >600 370 6.2Ni50Mn30 15 0.02 250 300 6.8 CrMnPt 15 0.02 200 240 6.9 Spin valve filmswith IrMn, RhMn, RhRuMn or CrMnPt: heat-treated at 270° C. for 1 hour.Spin valve films with PtMn or NiMn: heat-treated at 270° C. for 10hours.

TABLE 7 Spin Valve Film Constitution: Substrate/5 nanometerTa/NiFe/CoFe/3 nm Cu/2.5 nm CoFe/antiferromagnetic layer/5 nanometer TaAntiferromagnetic Blocking Resistance Layer J Temperature ChangeThickness (erg/cm²) H_(UA) (Oe) Tb Rate ΔR/R Material (nm) at 200° C. at200° C. (° C.) (%) Ir22Mn78 5 0.04 170 250 6.6 10 0.045 190 290 6.2Pt51Mn49 10 0.03 130 300 7.2 20 0.1 430 350 6.7 30 0.12 510 370 6.4 Spinvalve films with IrMn: heat-treated at 270° C. for 1 hour. Spin valvefilms with PtMn: heat-treated at 270° C. for 10 hours.

TABLE 8 Half-value Width of the diffraction peak from the close- packedAntiferromagnetic Layer plane in Blocking Thickness its rocking J(erg/cm²) Temperature Material (nm) curve, Δθ at 200° C. Tb (° C.)Ir22Mn78 5 12 0.1 210 5 8 0.025 230 5 5 0.045 250 5 3 0.05 250 Rh20Mn807 13.5 ~0 190 7 8 0.02 225 7 4 0.025 235

As in Table 6 and Table 8, we, the present inventors have found that (1)when the pinned magnetic layer as coupled to the antiferromagnetic layerhas a structure of SyAF and when the composition of theantiferromagnetic layer is specifically selected, then the magneticcoupling coefficient J at 200° C. could be at least 0.02 erg/cm², (2)when the close-packed plane of the antiferromagnetic layer is sooriented that the half-value width of the diffraction peak from theclose-packed plane of the layer in its rocking curve is reduced,preferably so that it appears at 8 degree or smaller, more preferably at5 degrees or smaller, then the magnetic coupling coefficient J at 200°C. could be increased, (3) when the magnetic thickness of theantiferromagnetic layer is not larger than 20 nanometers, morepreferably not larger than 10 nanometers, then the resistance changerate in the spin valve device having a multi-layered, pinned magneticlayer structure could be increased to be comparable to or higher thanthat in the spin valve device having a single-layered, pinned magneticlayer structure, and (4) when the magnetic coupling coefficient J at200° C. is at least 0.02 erg/cm², then the magnetic coupling biasH_(UA)* at 200°0 C. could be at least 200 Oe, and, therefore, eventhough the maximum magnetic field to be applied to the reproductiondevice, spin valve film, from a recording medium or the like is 200 Oe,the pinned magnetic layer in the spin valve film is still kept stable.On the basis of these findings, we have completed the present invention.

FIG. 18 is a schematic view of the magnetic coupling bias field HUA*versus the change in the resistance of the spin valve film depending onthe applied magnetic field. In FIG. 18, the magnetic coupling bias fieldH_(UA)* is defined as the maximum magnetic field at which themagnetization of the pinned magnetic layer does not substantially move,and this is obtained as the intersection of the extended line from thelinear region in the low magnetic field side and the extended line fromthe linear region in the high magnetic field side. The magnetization ofthe pinned magnetic layer having a magnetic coupling bias field H_(UA)*of at least 200 Oe moves little within the magnetic field range up to200 Oe in the resistance-magnetic field characteristics for which anexternal magnetic field is applied to the magnetization pinneddirection, and only the free layer responses to the magnetization togive resistance change.

In FIG. 18, seen is only the steep resistance change resulting from themagnetization response of the free layer in the vicinity of the magneticfield of zero which is the operating point for a magnetic field sensor,on the resistance-magnetic field characteristic curve. In this, noresistance change is admitted except the magnetization response of thefree layer to the applied magnetic field of up to 200 Oe. After the freelayer has been saturated, there occurs no substantial response to themagnetic field.

When conventional antiferromagnetic layers of NiO or FeMnCr are used,the constant J could not obtained little at 200° C. On the other hand,when an antiferromagnetic layer of CrMnPt having a thickness of 30nanometers, the resistance change rate is lower than that inconventional pinned magnetic layers having a single-layered structure,and the layer of CrMnP of that type is unfavorable.

As in Table 7 showing the data of conventional pinned magnetic layershaving a single-layered structure, PtMn gives high H_(UA)* when itsthickness is at least 20 nanometers but its resistance change rate fallsbetween 6.4 and 6.7% and is relatively low.

As opposed to those, in the samples of the invention shown in Table 6 inwhich the antiferromagnetic layer is of any of IrMn, RhMn, RhRuMn, PtMn,NiMn or CrMnPt having a thickness of at most 20 nanometers, H_(UA)* at200° C. is at least 200 Oe, or that is, these samples have excellentthermal stability. In addition, the resistance change rate in thosesamples is comparable to or higher than that in the conventional sampleswhere the pinned magnetic layer has a single-layered structure. In theinvention, the lowermost limit of the thickness of the antiferromagneticlayer is preferably at least 3 nanometers.

FIG. 19 is a graph of the angle of movement of the magnetization of themulti-layered, pinned magnetic layer of spin valve films of theinvention with H_(UA)* of 200 Oe and that of the single-layered, pinedmagnetic layer of conventional spin valve films with H_(UA) of 500 Oe,versus time, in the presence of a bias field of 200 Oe at 200° C.perpendicular to the direction of the pinned magnetization. As in FIG.19, it is understood that the time-dependent change at 200° C. in thepinned magnetization in the spin valve films of the invention is smallerthan that in the pinned magnetization in the conventional spin valvefilms where the pinned magnetic layer has a single-layered structure,even though H_(UA)* at 200° C. in the former is 200 Oe and is smallerthan that in the latter of being 510 Oe. This means that the spin valvefilms of the invention are stable.

The resistance change rate in the spin valve films of the inventionwhere the antiferromagnetic layer is of an Mn-rich, γ-Mn basedantiferromagnetic material such as IrMn, RhMn or RhRuMn and has athickness of at most 10 nanometers is larger than that in theconventional spin valve films incorporating a single-layered, pinnedmagnetic layer. Those spin valve films of the invention are morepreferred.

As in Table 6, the spin valve films of the invention with theantiferromagnetic layer having Tb of from 240 to 300° C. have goodthermal stability for the magnetization pinning. Therefore, in thosespin valve films of the invention, since both the ferromagnetic layer Aand the ferromagnetic layer B could be saturated in the same directionby applying thereto a magnetic field larger than the coupling magneticfield of the antiferromagnetically coupling layer at around Tb tothereby freely control the magnetization direction of the pinnedmagnetic layer by the applied magnetic field, the intended magnetizationpinning can be realized even at a temperature not higher than 300° C. atwhich the diffusion between the antiferromagnetically coupling layer andthe ferromagnetic layers A and B could be negligible.

In order to prevent the diffusion between the antiferromagneticallycoupling layer and the ferromagnetic layers A and B and to retard theinfluences of the diffusion, it is desirable that theantiferromagnetically coupling layer has a thickness of larger than 0.8nanometers and contains any of Ru, Rh, Cr, Ir or the like. For thatpurpose, it is effective to use a Co alloy such as CoFe for theferromagnetic layers A and B and to make the level of the surfaceroughness of the antiferromagnetically coupling layer comparable to orlower than the thickness of the layer itself.

In the thermal treatment for settling the magnetization direction of thepinned magnetic layer, both the magnetic layers A and B must besaturated in the same direction. Therefore, if the ferromagnetic layersA and B are so thinned that their thickness is around 2 nanometers andwhen the thickness of the antiferromagnetically coupling layer is notlarger than 0.8 nanometers, the antiferromagnetically coupling magneticfield of the coupling layer will increase up to about 7 kOe or larger.In that condition, the thermal treatment for settling the magnetizationdirection of the pinned magnetic layer would be difficult in apracticable external magnetic field. For these reasons, it is desirablethat the thickness of the antiferromagnetically coupling layer is largerthan 0.8 nanometers. With such a thick coupling layer, the thermaltreatment for settling the magnetization direction of the pinnedmagnetic layer could be attained in a practicable external magneticfield of, for example, 7 koe.

In the samples of the invention in Table 6 all with an SyAF-typeantiferromagnetically coupling layer, the thickness of the ferromagneticlayers A and B of a CoFe alloy is 2.5 nanometers each, and that of theantiferromagnetically coupling layer of Ru is 0.9 nanometers. In those,the antiferromagnetically coupling magnetic field is around 4 kOe, andgood thermal stability could be ensured to the pinned magnetic layer insuch an antiferromagnetic field.

In the device of the invention, it is desirable that the magneticthickness of the ferromagnetic layer A is nearly the same as or largerthan that of the ferromagnetic layer B. In the device where the magneticthickness of the ferromagnetic layers A and B is nearly the same, themagnetization of the pinned magnetic layer is much more stable againstthe ambient magnetic field and against the longitudinal bias magneticfield than in the device where the magnetic thickness of theferromagnetic layer A is larger than that of the ferromagnetic layer B.

On the other hand, the device where the magnetic thickness of theferromagnetic layer A is larger than that of the ferromagnetic layer Bcould have better ESD resistance with little pinning magnetizationreversal owing to ESD, than that where the magnetic thickness of theferromagnetic layers A and B is nearly the same. In the former case, itis desirable that the ratio of the magnetic thickness of theferromagnetic layer B to that of the ferromagnetic layer A falls between0.7 and 0.9. For example, when the ferromagnetic layer A is of a CoFealloy of 2.5 nanometers thick, then the ferromagnetic layer A ispreferably of a CoFe alloy of 2 nanometers thick. Even though themagnetic thickness of the ferromagnetic layers A and B is nearly thesame, and even when ESD occurs to cause pinning magnetization reversal,repinnable magnetic disc drives could be realized by incorporatingthereinto a circuit capable of repinning the magnetization of the pinnedmagnetic layer in a predetermined direction in the presence of currentforce (for example, U.S. Pat. No. 5,650,887). For realizing the value Jat 200° C. of at least 0.02 erg/cm², it is desirable to employ anantiferromagnetic layer comprising, as the major phase, a γ-Mn phase ofIrMn, RhMn, RhRuMn or the like or a ordered AuCUII-type phase thatconsists essentially of Mn (of which the Mn content is more preferablyfrom more than 0 but less than 40%); or to employ an antiferromagneticlayer comprising a ordered, face-centered cubic system phase (of CuAuItype) of PtMn, PtPdMn, NiMn or the like (of which the Mn content is morepreferably from 40 to 70%); or to employ a Cr-based antiferromagneticlayer of CrMn, CrAl or the like.

For ensuring a high value J at 200° C. of at least 0.02 erg/cm² to thosealloys in thin antiferromagnetic layers capable of attaining a highresistance change rate, the alloys must have a crystal structure with anoriented close-packed plane.

From the data in Table 8 that indicate the relationship between thehalf-value width Δθ of the diffraction peak from the close-packed planeof the antiferromagnetic layer in its rocking curve (this is a parameterof the close-packed plane orientation), Tb and J, it is understood thatthe spin valve films of the invention have a value of J of at least 0.02erg/cm² when the half-value width Δθ is not larger than 8 degrees.Therefore, it is understood that using those spin valve films realizesthe intended magnetoresistance effect heads of the invention. Even forthe antiferromagnetic layer of PtMn or the like having a ordered,face-centered cubic system phase or for the bcc-type antiferromagneticlayer of CrMn or the like, the layer could have a high Tb and a high Jat 200° C. even if it is thin, so far as the close-packed plane thereinis oriented in the same manner as above. The close-packed plane asreferred to herein is meant to indicate the (111) peak for the fccphase, the (002) peak for the hcp phase, and the (110) peak for the bccphase. In the case of PtMn or the like containing a ordered,face-centered cubic system phase, the remaining fcc phase shall beoriented in the (111) plane, or the (111) plane of the ordered,face-centered cubic system phase shall be oriented. The fcc phase andthe hcp phase may have lamination defects.

As in FIG. 20, the half-value width of the diffraction peak from theclose-packed plane of the layer in its rocking curve could berepresented by the fluctuation of the close-packed plane spots in thedirection perpendicular to the film surface in the transmission electronmicroscopic images of the cross section of the head, and the half-valuewidth in the rocking curve in X-ray diffractiometry nearly correspondsto the fluctuation angle of the close-packed plane spots in thetransmission electron microscopic images.

To realize such good close-packed plane orientation, the spin valvefilms may be formed in an atmosphere with impurities such as oxygen gasand others therein being minimized as much as possible. For example, forforming the films, employable are a deposition method in which is usedan apparatus capable of pre-degassing the system to a level of around10⁻⁹ Torr; a deposition method in which is used a sputtering target ofwhich the oxygen content is lowered to at most 500 ppm; a substrate biassputtering method in which a controlled degree of energy is applied tothe sputtered atoms while the atoms are deposited on the substrate; anda deposition method in which a underlayer of a simple noble metal of,for example, Au, Cu, Ag, Ru, Rh, Ir, Pt, Pd or the lie, or a underlyaerof an alloy of any of those noble metals, of an Ni-based alloy layer ofNiFe, NiCu, NiFeCr, NiFeTa or the like is provided between the aluminagap layer and the spin valve film.

The above is to explain the outline of the technical field common to thesecond to sixth embodiments of the invention as directed to the“improvement in the thermal stability and the reproduction outputpower”.

The second to sixth embodiments of the invention are described in detailhereunder.

Second Embodiment

FIG. 17 shows one example of the magnetoresistance effect head of thisEmbodiment. As in FIG. 17, a lower shield 11 and a lower gap film 12 areformed below an AlTiC (Al₂O₃TiC) substrate, and a spin valve device 13is formed thereon. The lower shield 11 may be of NiFe, a Co-basedamorphous magnetic alloy, an FeAlSi alloy or the like having a thicknessof from 0.5 to 3 μm, and it is desirable that NiFe or the FeAlSi alloy,if used, is polished to remove surface roughness. The lower gap layer 12may be of alumina or aluminium nitride having a thickness of from 5 to100 nanometers.

The spin valve device comprises a spin valve film 14, a pair oflongitudinal bias films 15 and a pair of electrodes 16. The spin valvefilm comprises a nonmagnetic underlayer 141 of Ta, Nb, Zr, Hf or thelike having a thickness of from 1 to 10 nanometers, an optional secondunderlayer 142 having a thickness of from 0.5 to 5 nanometers, anantiferromagnetic layer 143, a pinned magnetic layer 144, an interlayer145 having a thickness of from 0.5 to 4 nanometers, a free layer 146,and an optional protective film 147 having a thickness of from 0.5 to 10nanometers.

Above the spin valve device, formed are a gap layer 17 and an uppershield 11. Though not shown, a recording part is formed over them. Thegap layer may be of alumina or aluminium nitride having a thickness offrom 5 to 100 nanometers; and the upper shield 18 may be of NiFe, aCo-based amorphous magnetic alloy, an FeAlSi alloy or the like having athickness of from 0.5 to 3 μm.

Where the antiferromagnetic layer 143 is of a γ-Mn-based, Mn-rich alloyof IrMn, RhMn, RhRuMn or the like, or of a ordered, face-centered cubicsystem alloy of PtMn, NiMn or the like, it is desirable that theunderlayer 142 is of a metal film of, for example, Cu, Ag, Pt, Au, Rh,Ir, Ni or the like, or an alloy consisting essentially of those metalssuch as AuCu, CuCr or the like; Ni, an Ni-based alloy, NiFe, anNiFe-based alloy or the like such as those described in JP-A 9-229736;or Ru, Ti or the like, or an alloy consisting essentially of thosemetals.

Where the antiferromagnetic layer 143 is of a Cr-based antiferromagneticalloy film, the underlayer 142 may be any of those mentioned above. Forthe underlayer 142, also suitable is any of bcc-phase metals of Cr, V,Fe and the like, or of alloys consisting essentially of those metals.

The pinned magnetic layer 144 is of a three-layered film, whichcomprises two layers of a ferromagnetic layer B, 1441, and aferromagnetic layer A, 1443, as antiferromagnetically coupled to eachother via an antiferromagnetically coupling layer 1442 existingtherebetween. It is desirable to interpose a nonmetallic element such asoxygen, nitrogen or the like between the ferromagnetic layer B and theantiferromagnetic layer 143 or between the ferromagnetic layer B and thelongitudinal bias film of the antiferromagnetic film, as producing largeresistance change. In that case, the thickness of the interlayer intowhich the nonmetallic element is incorporated is preferably from 0.2 to2 nanometers. For example, preferred is a structure of ferromagneticlayer A (or ferromagnetic layer B)/oxide layer/ferromagnetic layer B (orferromagnetic layer A) in which an oxide interlayer is disposed betweenthe ferromagnetic layers A and B.

The antiferromagnetically coupling layer 1442 may be of a metal of Ru,Rh, Ir or Cr. Preferred are Ru having an extremely largeantiferromagnetically-coupling function; Ru capable of exhibiting itsantiferromagnetically-coupling function in a broad film thickness range;and Cr capable of exhibiting its antiferromagnetically-coupling functionin a broad film thickness range. The thickness of theantiferromagnetically coupling layer is not specifically defined,provided that it is suitable for making the layer exhibit itsantiferromagnetically-coupling function. For this, referred to is thedisclosure in Phy. Rev. Lett., 67, (1991), 3598.

FIG. 21 is a graph of residual magnetization ratio, Mr/Ms, indicatingthe reduction in the antiferromagnetic coupling capability of theantiferromagnetically coupling layer of Ru after thermal treatment,relative to the thickness of the Ru layer. In this, theantiferromagnetic coupling layer of Ru is to couple a ferromagneticlayer of Co and a ferromagnetic layer of a CoFe alloy. Mr/Ms=1 meansthat the coupling layer of Ru has completely lost its antiferromagneticcoupling capability; and Mr/Ms=0 means that the antiferromagneticcoupling of the ferromagnetic layers by the coupling layer of Ru is in acomplete condition.

As in FIG. 21, it is understood that the thickness of theantiferromagnetic coupling layer of Ru is preferably from more than 0.8nanometers up to 1.2 nanometers. With its thickness falling within thedefined range, the characteristics including theantiferromagnetically-coupling function of the antiferromagneticcoupling layer of Ru are not degraded in any thermal treatment at 250 to300° C. which may be needed for settling the magnetization direction ofthe pinned magnetic layer 144 or may be needed in any other steps offabricating heads and which often induces mutual diffusion between thecoupling layer and the neighboring ferromagnetic layers B and A. If thethickness of the Ru layer is not larger than 0.8 nanometers, someattention must be paid to the mutual diffusion to cause the degradationof the antiferromagnetically-coupling function of the Ru layer. On theother hand, if the thickness is larger than 1.2 nanometers, theantiferromagnetic coupling of the layers B and A by the Ru layer will bedifficult. Where the antiferromagnetically coupling layer is of Cr, itsthickness is also preferably from more than 0.8 nanometers up to 1.2nanometers for the same reasons as those for the Ru layer. Theferromagnetic layers B and A are preferably of Co or a Co-based alloy.

Where the ferromagnetic layers B and A are of a Co_(1−x)Fe_(x) alloy(0<×≦0.5), a large magnetic coupling coefficient could be ensured tothem with the antiferromagnetic layer 143 of a γ-Mn-based, Mn-rich alloyof IrMn, RhMn, RhRuMn or the like, and, in addition, the mutualdiffusion between Ru and the ferromagnetic layers B and A could beprevented. Therefore, the alloy is favorable to the layers B and A. IfCo is used for the layers B and A in place of the CoFe alloy, J will bearound ⅔. In addition, as in FIG. 21, the thickness range of theantiferromagnetically coupling layer capable of still maintaining thestable antiferromagnetically-coupling function even after thermaltreatment at 270° C. for 1 hour or so is narrowed for the Co layers, ascompared with that for the CoFe layers.

The surface smoothness of the antiferromagnetically coupling layer isalso important for the purpose of maintaining the thermal stability forthe antiferromagnetically-coupling function of the layer. If the levelof the surface roughness of the layer is larger than the thickness ofthe layer itself even in a minor region of 10 nm² or so, the thermalstability for the antiferromagnetically-coupling function of the layerwill be lowered. Therefore, it is desirable that the level of thesurface roughness of the antiferromagnetically coupling layer is notlarger than the thickness of the layer itself.

Table 9 shows the variation in the sheet resistance Rs of spin valvefilms, the sheet resistance change ΔR and the resistance change rateΔR/R, relative to the varying thicknesses of the ferromagnetic layers Aand B. FIG. 22A, FIG. 22B and FIG. 22C are graphs of resistance changein spin valve films versus the applied magnetic field.

TABLE 9 Spin Valve Film Constitution: Ta/Au/CuMn/ferromagnetic layer A(CoFe)/0.9 nm Ru/ferromagnetic layer B (CoFe)/2.5 nm Cu/free layer (4 nmCoFe)/Ta Thermal treatment: at 270° C. for 1 hour Thickness Thickness ofof Sheet Ferromagnetic Ferromagnetic Resistance Sheet resistance Layer ALayer B Change Rate resistance Change (nm) (nm) ΔR/R (%) Rs (Ω) ΔRs (Ω)7 7 7.2 7.5 0.54 5 5 8.0 9.8 0.78 3 3 8.6 12 1.03 2 2 8.4 14.1 1.18 1 18.0 15.3 1.22 0.5 0.5 5.9 15.6 0.92

As in Table 9, the thicknesses of the ferromagnetic layers B and A arepreferably from 1 to 5 nanometers for obtaining a high resistance changerate, but more preferably from 1 to 3 nanometers. With the layers B andA each having a thickness to fall within the preferred range, the pinnedmagnetic layer is stable to the applied magnetic field (that is, theresistance decreases only a little even in the applied magnetic field of+600 Oe), as in FIGS. 22A to 22C, and, in addition, the sheet resistanceRs of the spin valve films is high and the sheet resistance change ΔRsis on a satisfactory level. The reproduction output is proportional tothe product of the sense current and the resistance change, and theresistance change is proportional to the product of the resistancechange rate and the sheet resistance of the spin valve film. Therefore,the cases in which only the resistance change rate is large could notproduce high output if their sheet resistance is small. In other words,in order to attain high output, both the resistance change rate and thesheet resistance must be high.

FIG. 23A, FIG. 23B and FIG. 23C are graphs of resistance change in spinvalve films in which the thickness of the ferromagnetic layer A is fixedto be 3 nanometers and that of the ferromagnetic layer B is varied,versus the applied magnetic field.

As in FIGS. 23A to 23C, when the thickness of the ferromagnetic layer Ais the same as that of the ferromagnetic layer B, the resistance changein the spin valve film in a high magnetic field of +600 Oe is small. Inthat case, therefore, the pinned magnetic layer is extremely stable tothe ambient magnetic field, to the magnetic field from the longitudinalbias layers and to the applied magnetic field in thermal treatment forforming the recording part. As so mentioned hereinabove, the problem ofmagnetization reversal in the pinned magnetic layer to be caused by ESDcould be solved by the current circuit as incorporated in the drive andcapable of correcting the pinning magnetization direction to be in apredetermined direction.

On the other hand, the different thicknesses of the ferromagnetic layersA and B have the following advantages: The first is that the thermaltreatment for magnetization pinning is easy, which is indispensable forensuring the basic constitution of the spin valve film where themagnetization of the free layer is perpendicular to that of the pinnedmagnetic layer. The second is that, when the thickness of theferromagnetic layer B is smaller than that of the ferromagnetic layer A,the resistance change rate is increased, as in Table 10 showing therelationship between the varying thickness of the ferromagnetic layer Band the resistance change rate. The third is that the magnetizationreversal to be caused by ESD occurs little in the pinned magnetic layer,and stable reproduction output is possible even high voltage of aroundthe breakdown voltage. The breakdown voltage as referred to herein ismeant to indicate the voltage at which the spin valve device is brokenand the spin valve device resistance begins to increase.

TABLE 10 Spin Valve Film Constitution: 5 nanometer Ta/2 nm AuCu/5 nmCoFe/3 nm Cu/ferromagnetic layer A (CoFe)/0.9 nm Ru/ferromagnetic layerB (CoFe)/10 nm IrMn/5 nanometer Ta Thickness of Thickness of ResistanceChange ferromagnetic Layer ferromagnetic Layer Rate A (nm) B (nm) ΔR/R(%) 3 3 7.3 3 2.5 7.8 3 2 7.7

For example, when the ferromagnetic layer A, the ferromagnetic layer andthe free layer are of any of Co, CoFe and NiFe, while the nonmagneticspacer layer is of Cu, and when the ratio of the magnetic thickness ofthe layer A to that of the layer B is varied within a range between 0.7and 0.9 while the thickness of the ferromagnetic layer B is 2.5nanometers, then the spin valve films have good ESD resistance, as inFIGS. 24A and 24B, FIGS. 25A and 25B and Table 11. FIGS. 24A and 24B,and FIGS. 25A and 25B are graphs of resistance versus output in spinvalve devices to which has been applied a simulation ESD voltage by ahuman body model. In FIGS. 24A and 24B, the thickness of theferromagnetic layer A is the same as that of the ferromagnetic layer B;and in FIGS. 25A and 25B, the former is larger than the latter. Table 11shows the ESD data of spin valve devices in test patterns.

TABLE 11 Spin Valve Film Constitution: 5 nanometer Ta/free layer/3 nmCu/ferromagnetic layer A/0.9 nm Ru/ferromagnetic layer B/10 nm IrMn/5nanometer Ta Device Constitution: lead-overlaid structure (with noshield) Subbing hard film/longitudinal bias of CoPt/FeCo is formed onthe non-patterned lower shield and lower cap, and the electrode spacingis narrower than the longitudinal bias spacing. Electrode spacing = 1.3μm Magnetic Thickness Spinning Ratio Magnetization (Ms · t)A/Ferromagnetic Ferromagnetic Free Reversal Breakdown (Ms · t)B Layer ALayer B Layer Voltage Voltage 0.75   2 nmCoFe 1.5 nmCoFe   3 nmCoFe/ not70 V 1.5 nmNiFe reversed 0.8 2.5 nmCoFe   2 nmCoFe   3 nmCoFe/ not 75 V1.5 nmNiFe reversed 0.83   3 nmCoFe 2.5 nmCoFe   4 nmCoFe/ not 70 V 1.8nmNiFe reversed 0.85   2 nmCoFe 1.7 nmCo 0.5 nmCoFe/ not 70 V   4 nmNiFereversed 0.71 2.4 nmCoFe 1.7 nmCoFe   1 nmCoFe/ 65 V 75 V   3 nmNiFe0.88 2.4 nmCoFe 2.1 nmCoFe   1 nmCoFe/ 65 V 75 V   3 nmNiFe 1   3 nmCoFe  3 nmCoFe   4 nmCoFe/ 50 V 75 V 1.8 nmNiFe 0.667   3 nmCoFe   2 nmCoFe  3 nmCoFe/ 55 V 75 V 1.5 nmNiFe 0.93   3 nmCoFe 2.8 nmCoFe   1 nmCoFe/55 V 70 V   3 nmNiFe

In ESD, a magnetic field essentially of the current magnetic field isapplied to the pinned magnetic layer in such manner that the magneticfield intensity to the ferromagnetic layer B is larger than that to theferromagnetic layer A, while, on the other hand, the current magneticfield ratio, H(current)_(B)/H(current)_(A) is nearly equal to theinverse ratio of magnetic thicknesses, (Ms·t)_(A)/(Ms·t)_(B). In thatcondition, therefore, the magnetic energy changes due to the ESD currentfield of the ferromagnetic layers A and B cancel, thereby resulting inthat the total energy change of:{(Ms·t)·H(current)}_(A)−{(MS·t)·H(current)}_(B)is reduced. As a result, the magnetization of the pinned magnetic layercould not be moved in the ESD current magnetic field.

As in FIG. 23C, when the ferromagnetic layer A is 3 nanometers thick andthe ferromagnetic layer B is 2 nanometers thick and therefore(MS·t)_(B)/(MS·t)_(A)=0.67, then H_(UA)* is lower than that in the caseof FIG. 23A where both the ferromagnetic layers A and B are 3 nanometersthick, and therefore, the thermal stability of the pinned magnetic layerin the case of FIG. 23C is lower than that in the case of FIG. 23A. Inthat case where the magnetic thickness of the ferromagnetic layer B issmaller than that of the ferromagnetic layer A, it is desirable that thecurrent flow direction of the sense current to the pinned magnetic fieldis so selected that the magnetic field from the sense current is in thesame direction as that of the direction of the bias magnetic field fromthe antiferromagnetic field to be applied to the ferromagnetic layer B(or that is, in the same direction as the magnetization direction of theferromagnetic layer B). The reason is because, when the magneticthickness of the ferromagnetic layer A is larger than that of theferromagnetic layer B, a stray magnetic field that corresponds to themagnetic thickness difference between the ferromagnetic field and theferromagnetic field is applied to the free layer, like in conventionalspin valve films having a single-layered pinned magnetic layer, and, asa result, the perpendicular magnetization configuration of the freelayer and the pinned magnetic layer is disturbed by that stray magneticfield. This causes the problem of asymmetry of the reproduction waves,thereby bringing about reproduction output reduction. The stray magneticfield could be canceled by applying a sense current in such a mannerthat the magnetic field by the sense current could be in the samedirection as the direction of the magnetic coupling bias magnetic field,as in FIG. 26 which shows the magnetization and the stray magnetic fieldin spin valve films.

It is desirable that a simple metal of Cu, Au or Ag or an alloyconsisting essentially of those metals is used for the nonmagneticspacer layer. Basically, the thickness of the nonmagnetic spacer layermay well be in a range between 1 and 10 nanometers or so, capable ofensuring the necessary resistance change rate. Especially in the spinvalve films of the invention, it is desirable that the thickness of thenonmagnetic spacer layer falls between 1.5 nanometers and 2.5nanometers, as being able to control the interlayer-coupling magneticfield that may be generated between the pinned magnetic layer and thefree magnetic layer, to the level of at most 15 Oe, and as being able toproduce a high resistance change rate.

For the free layer, employable is any of Co, a Co alloy such as CoFe,CoNi, CoFeNi or the like, or a laminate film of those metals and alloys.For example, employable is a laminate film composed of an NiFe alloylayer and a thin Co layer, in which the thin Co layer is to be adjacentto the nonmagnetic interlayer. It is desirable that the thickness of thefree layer falls between 1 and 10 nanometers.

Table 12 shows a varying thickness of the free layer versus theresistance change rate ΔR/R, in which the thickness of the pinnedmagnetic layer is fixed to be 2.5 nanometers. As in Table 12, it isunderstood that, in the invention, the thickness of the free layer ismore preferably from 2 to 5 nanometers, as giving high resistance changerates.

TABLE 12 Resistance Change Rate Resistance ΔR/R** (%) Change Rate(laminated Thickness of ΔR/R* (%) free layer Thickness of Ferromagnetic(single- with 1 nm Co Free Layer Layer A = Ferromagnetic layered freeadjacent to (nm) Layer B (nm) layer of CoFe) interlayer) 1 2.5 6.2 5.7 22.5 7.5 7.0 3 2.5 7.9 7.2 4 2.5 7.8 7.2 5 2.5 7.5 7.1 6 2.5 6.9 6.4 72.5 6.6 6.0 The ferromagnetic layers A and B have the same thickness andare both of CoFe.

Table 13 shows a varying thickness of the ferromagnetic layer A of thepinned magnetic layer versus the resistance change rate ΔR/R, in whichthe thickness of the free layer is fixed to be 4 nanometers. As in Table13, it is desirable that the thickness, t(F), of the free layer of from2 to 5 nanometer Thick and the thickness, t(P) of the ferromagneticlayer A satisfy the following condition:−0.33≦{t(F)−t(P)}/t(F)≦0.67,for producing a high resistance change rate.

TABLE 13 Thickness of Thickness of Ferromagnetic Resistance Free Layer,Layer A, t(P) Change Rate, t(F) (nm) (nm) ΔR/R (%) (t(F) − t(P))/t(F)4.5 1 4.7 0.78 4.5 1.5 6.9 0.67 4.5 2 7.1 0.56 4.5 3 7.9 0.33 4.5 4 7.70.11 4.5 5 7.3 −0.11 4.5 6 6.8 −0.33 4.5 7 5.9 −0.66 The free layer isof CoFe. The ferromagnetic layers A and B are both of CoFe. Thethickness of the ferromagnetic layer B is 3 nm.

For the protective film, used is any of metals of Ta, Nb, Zr, Cr, Hf,Ti, Mo, W and the like, or their alloys, or their oxides, nitrides, etc.Preferred are high-resistance protective films of metal oxides ornitrides, for example, NiFe oxides, aluminium oxides, tantalum oxidesand others, as giving high resistance change rates. Regarding itsthickness, it is desirable that the protective film is as thin aspossible and has a thickness of from 0.3 to 4 nanometers. This isbecause, as will be mentioned hereunder, such a thin protective film iseasy to remove through etching for forming electrodes and longitudinalbias layers. As the protective layer, also usable are single-layered orlaminated films of simple noble metals such as Ag, Au, Ru, Ir, Cu, Pt,Pd, Re and others, or of their alloys. For example, for the free layerof CoFe, usable are protective layers of Cu/Ru, Cu, Au, Cu alloys, etc.;for the free layer of NiFe, usable are protective layers of Ag, Ru,Ru/Ag, Ru/Cu, Cu, etc. Over the protective film of oxides, nitrides ornoble metals, an additional, high-resistance protective film of Ta orthe like may be optionally formed.

For making the magnetization direction of the pinned magnetic layerperpendicular to that of the free layer, for example, employable is thefollowing method. Where the antiferromagnetic layer 143 is of aγ-Mn-based, Mn-rich alloy such as IrMn, RhMn, RhRuMn or the like, thedeposition of the constituent layers of the spin valve film to theantiferromagnetically coupling layer 1442 is carried out in a magneticfield as applied in the direction of the width of the spin valve deviceto be produced, or that is, in the height direction, and thereafter theresulting layered structure is subjected to thermal treatment forunifying the coupling bias magnetic field due to the antiferromagneticlayer 143 in the height direction. The thermal treatment for unifyingthe coupling bias magnetic field in the height direction may be carriedout immediately after the formation of the antiferromagnetic layer B.However, since the antiferromagnetically coupling layer of Ru or thelike is more resistant to oxidation, it is more desirable that thethermal treatment is effected after the formation of the coupling layer1442. Preferably, the thermal treatment is effected still in vacuum, orthat is, without leaking the vacuum for the previous deposition, at atemperature higher than Tb and for a short period of time, morepreferably within at most 10 minutes, in a magnetic field in which theferromagnetic layer B could be completely saturated. For example, forIrMn having Tb of 300° C., the thermal treatment may be effected at 350°C. for 1 minute or so.

Next, still in vacuum, a magnetic field is applied in the direction ofthe track width of the spin valve device being formed, at least duringthe formation of the free layer, and thereafter, the remaining films ofthe spin valve device are formed. The same shall apply to the case wherethe antiferromagnetic layer is of a ordered alloy of PtMn or NiMn. Forthis case, however, the process will somewhat differ from that for thecase of the γ-Mn-based antiferromagnetic layer noted above. In thiscase, the deposition step up to the formation of the antiferromagneticlayer B does not always require a magnetic field, but the thermaltreatment after the step must be effected at high temperatures of atleast 200° C., preferably falling between 270 and 350° C., for a fewhours, preferably for 1 to 20 hours. After the thermal treatment, amagnetic field is applied during the step of forming the free layer andthereafter the remaining layers of the spin valve film are formed, inthe same manner as in the previous case.

In any case, the thermal treatment for the antiferromagnetic layer maybe effected after the formation of the spin valve film. When the thermaltreatment is effected after the film formation, it is desirable that amagnetic field higher than the coupling magnetic field of theantiferromagnetically coupling layer 1442 is applied to the spin valvefilm being subjected to the thermal treatment so that the magnetizationsof both the ferromagnetic layer A and the ferromagnetic layer B aresaturated completely in the same direction (that is, in the heightdirection). For example, where the antiferromagnetic layerB/antiferromagnetic layer B is in the form of 2 nm CoFe/0.9 nm Ru/2 nmCoFe, the coupling magnetic field of Ru is about 6 kOe. Therefore, inthis case, the magnetic field to be applied during the thermal treatmentis preferably at least 7 kOe. In order to reduce the magnetic field forthe thermal treatment, it is desirable to finish the thermal treatmentbefore the spin valve film is worked into the form of a device. Thethermal treatment of the device as worked from the film requires astronger magnetic field for saturating the ferromagnetic layers A and Bbecause of the reversal magnetic field intrinsic to the shape of thedevice.

In the method noted above, the magnetization of the pinned magneticlayer 144 is pinned in a predetermined direction. However, the heattreatment in the method is too strong, the easy axis of the free layer146 and even that of the lower shield 11 will also be pinned in theheight direction of the spin valve device, like in the pinned magneticlayer. If so, it will be difficult to make the magnetization directionof the free layer perpendicular to that of the pinned magnetic layer. Inorder to fix the easy axis of the free layer and that of the lowershield in the direction of the track width, it is desirable to apply tothe free layer and the shield, the minimum magnetic field necessary forsaturating the shield and the free layer in the direction of the trackwidth, for example, a magnetic field of from 100 to 300 Oe or so, in theresist curing step for fabricating recording heads, thereby stabilizingthe easy axis of the shield and that of the free layer in the directionof the track width. Also preferably, the lower shield is previouslysubjected to thermal treatment before the completion of the spin valvefilm, thereby stabilizing its easy axis in the direction of the trackwidth.

In the abutted junction type device of FIG. 17, in which the track edgesof the free layer are removed and longitudinal bias layers are providedin place of the removed edges, the longitudinal bias layers may be of ahard magnetic film of, for example, CoPt, CoPtCr or the like as formedon a underlayer of, for example, Cr, FeCo or the like, or may be of alaminated, hard ferromagnetic film composed of a ferromagnetic layer 151and an antiferromagnetic layer 152 as laminated in that order.Alternatively, the antiferromagnetic layer 152 may be formed first, andthereafter the ferromagnetic layer 151 may be laminated thereover. Inorder to obtain a steep reproduction sensitivity profile capable ofmeeting the coming narrow tracks in the art, at the track edges, it isdesirable that the magnetic thickness ratio of the ferromagnetic,longitudinal bias layer, or that is, the hard magnetic layer or theferromagnetic bias layer as magnetically coupled by an antiferromagneticlayer, to the free layer, (Ms·t)_(LB)/(Ms·t)_(F), is defined to be atmost 2. Where the free layer is thinned to have a thickness of from 2 to5 nanometers and have a magnetic thickness of from 3 to 6 nanometerTesla, the ferromagnetic, longitudinal bias layers shall also be thinnedin order that the ratio (MS·t)_(LB)/(MS·t)_(F) is made to be at most 2.For example, the ferromagnetic, longitudinal bias layer shall have amagnetic thickness of at most 12 nanometer Tesla.

In general, however, when the hard magnetic film is thinned to have athickness of 10 nanometers or so, then it could hardly maintain highcoercive force. For example, for a hard magnetic film of CoPt having Msof 1T, it has a high coercive force of 2000 Oe when its thickness is 20nanometers, but its coercive force decreases to 800 Oe when itsthickness is 10 nanometers. On the other hand, in the longitudinal biaslayer of a type of ferromagnetic layer/antiferromagnetic layer, themagnetic coupling bias field increases with the reduction in thethickness of the ferromagnetic layer 151, whereby the two layers arecoupled more firmly. For example, for the longitudinal bias layer havinga laminated structure of NiFe with Ms of 1T and IrMn of 7 nanometersthick, its coercive force is 80 Oe when its thickness is 20 nanometers,but increases up to 160 Oe when its thickness is 10 nanometers. Thevalue of 160 Oe is an effective value in conventional MR heads.Therefore, in the region where the free layer is thin, for example,having a thickness of at most 5 nanometers, it is desirable to employthe longitudinal bias layer of the type of ferromagneticlayer/antiferromagnetic layer.

In addition, in the longitudinal bias layer of the type of ferromagneticlayer 151/antiferromagnetic layer 152, it is further desirable that thesaturation magnetization of the ferromagnetic layer 151 is nearlycomparable to or larger than that of the free layer in order tocompletely remove the Barkhausen noise in a smallest possiblelongitudinal bias field. The ferromagnetic film 151 may be of an NiFealloy, but is more preferably of an NiFeCo alloy, a CoFe alloy, Co orthe like having a larger saturation magnetization. If a film having asmall saturation magnetization is used for the ferromagnetic film 151and if the Barkhausen noise is removed by increasing its thickness toenlarge the stray magnetic field, the reproduction output will lowerespecially in narrow track width.

In FIG. 17, the longitudinal bias layers are formed without completelyremoving the entire spin valve film. Apart from the illustrated case,even the underlayer 141 may be removed through etching. However, inorder to maintain good crystallinity of the ferromagnetic layer, it isdesirable that the etching depth before the formation of thelongitudinal bias layers is at most above the underlayer 142 so as totake advantage of the crystallinity-improving effect of the layer 142.From the viewpoint of film thickness control, it is desirable that thethicker antiferromagnetic layer 143 is etched in some degree andthereafter the magnetic coupling bias is attenuated so as to obtain,longitudinal bias layers having good hard magnetic properties. As thecase may be, after the nonmagnetic spacer layer is partly etched, and alongitudinal bias layers of ferromagnetic film 151/antiferromagneticfilm 152 may be formed thereover. For the purpose of improving thecrystallinity or for the purpose of attenuating the magnetic couplingbetween the pinned magnetic layer or the antiferromagnetic layer 143 andthe longitudinal bias layer, an extremely thin underlayer 153, like theunderlayer 143, may be provided below the ferromagnetic film 151. Forthe purpose of minimizing the reduction in the magnetic coupling betweenthe free layer and the longitudinal bias layer, the thickness of theunderlayer 153 is preferably at most 10 nanometers.

Where the hard magnetic film is employed, it is also desirable that thesaturation magnetization of the free layer is comparable to that of thehard magnetic layer. In general, however, it is difficult to prepare ahard magnetic film having high saturation magnetization that iscomparable to the free layer of CoFe or the like generally having highsaturation magnetization. For this, effective is a method of using asubbing film of FeCo or the like having high saturation magnetizationfor the hard magnetic film to thereby keep the good balance ofsaturation magnetization between the subbed hard magnetic film and thefree layer, for the purpose of removing the Barkhausen noise in a smalllongitudinal bias magnetic field.

For the antiferromagnetic film 152, employable is the sameantiferromagnetic substance as that for the spin valve film. However,the magnetic coupling bias field for the antiferromagnetic layer in thespin valve film is in the height direction while that for theantiferromagnetic film 152 in the longitudinal bias layer is in thetrack width direction, or that is, the two must be perpendicular to eachother. Therefore, for example, the two are made to have a differentblocking temperature Tb, and the magnetic coupling bias direction of theantiferromagnetic layer having a higher Tb is first settled throughthermal treatment, and thereafter the antiferromagnetic film having alower Tb is subjected to thermal treatment at lower temperatures. Inthat condition, while the magnetic coupling bias direction of theantiferromagnetic layer having a higher Tb is kept stable as it is, themagnetic coupling bias direction of the antiferromagnetic film having alower Tb is settled, whereby the magnetic coupling bias fields of thetwo could be made perpendicular to each other.

Concretely, the antiferromagnetic film 152 may be an antiferromagneticfilm of PtMn, PdPtMn or the like capable of expressing H_(UA) throughthermal treatment. For this, however, more preferred is any of RhMn,IrMn, RhRuMn, FeMn or the like having Tb of from 200 to 300° C., sincethey can be subjected to thermal treatment at temperatures at which thepinned magnetic layer is stable. For the antiferromagnetic layer in thespin valve film, preferred are antiferromagnetic substances having ahigher Tb, such as IrMn, PtMn, PtPdMn, etc. Using those preferredantiferromagnetic substances, the magnetic coupling bias direction ofthe antiferromagnetic film 152 could be well settled in the track widthdirection without disturbing the magnetization direction of the pinnedmagnetic layer in the spin valve film in the step of thermal treatmentfor resist curing noted above. Specifically, because of thecharacteristic of the invention where the pinning magnetization israpidly stabilized at temperatures not higher than the blockingtemperature, the longitudinal bias and the magnetization of the pinnedmagnetic layer could be made well perpendicular to each other eventhough the difference in the blocking temperature between the bothantiferromagnetic films is only tens ° C. When IrMn, FeMn, RhMn, RhRuMn,CrMnPt, CrMn or the like capable of producing a magnetic coupling biasfield during deposition them in a magnetic field is used for theantiferromagnetic film 152, it does not require any additional thermaltreatment. Therefore, the antiferromagnetic film 152 of any of thosesubstances, not requiring additional heat treatment, does not disturbthe bias magnetic field direction of the antiferromagnetic layer 143 inthe spin valve film. To be combined with the film 152 of that type, anyand every type of antiferromagnetic substances could be used for theantiferromagnetic layer 143 in the spin valve film, and in anycombination of the two, the longitudinal bias direction and themagnetization direction of the pinned magnetic layer could be made wellperpendicular to each other.

On the other hand, as in FIG. 27, only the protective film 147 at thetrack edges of the free layer may be etched away, and anantiferromagnetic film may be laminated thereover through magneticcoupling to apply a longitudinal bias to the free layer. In this case,it is desirable that the longitudinal bias layer 15 comprises anantiferromagnetic layer 152 and a buffer layer 1511, which is aunderlayer for enhancing the magnetic coupling with the free layer. Thebuffer layer 1511 is preferably a ferromagnetic layer of Fe, Co, Ni orthe like. For settling the magnetization direction of the longitudinalbias in this case, the same as in the above-mentioned case offerromagnetic layer 151/antiferromagnetic layer 152 could apply also tothis case. The longitudinal biasing system using such a ferromagneticlayer is advantageous in that the Barkhausen noise is effectivelyremoved therein, without generating any unnecessary longitudinal biasmagnetic field to lower the sensitivity of heads as in the system usinga hard magnetic film.

Third Embodiment

FIG. 28 shows the third embodiment of the invention. In FIG. 28, thestructure of the spin valve film differs from that in FIG. 21. In FIG.27, a spin valve film 14 formed on a lower gap 12, and comprises anonmagnetic underlayer 141 of Ta, Nb, Zr, Hf or the like having athickness of from 1 to 10 nanometers, an optional second underlayer 142having a thickness of from 0.5 to 5 nanometers, a free layer 146, aninterlayer 145 having a thickness of from 0.5 to 4 nanometers, a pinnedmagnetic layer 144, an antiferromagnetic layer 143, and an optionalprotective film 147 having a thickness of from 0.5 to 10 nanometers. Inthis, free layer 146, the interlayer 145, the pinned magnetic layer 144and the antiferromagnetic layer 143 are the same as those in the secondembodiment.

Where the underlayer 142 is of Au, Cu, Ru, Cr, Ni, Ag, Pt or Rh, or analloy consisting essentially of those metals, the thermal stability forthe resistance change rate could be increased especially when the freelayer is of a CoFe alloy.

In FIG. 27, a pair of longitudinal bias layers 15 and a pair ofelectrodes 16 which are the same as those in FIG. 21 constitute, alongwith the spin valve film 14, a spin valve device 13 Like in FIG. 21, anupper gap layer 17 and an upper shield 18 are formed to cover the device13.

Fourth Embodiment

FIG. 29 shows still another embodiment of the invention, which isapplied to a dual-type spin valve structure.

In FIG. 29, a pair of longitudinal bias layers 15, a pair of electrodes16, a longitudinal bias layer 15, and a spin valve device 13 comprisinga spin valve film 14 are formed on a lower shield 11 and a lower gap 12,and an upper gap 17 and an upper shield 18 are formed over them, like inFIG. 21 for the second embodiment and in FIG. 27 for the thirdembodiment. However, the structure of FIG. 29 differs from those of FIG.21 and FIG. 27 in point of the spacing between the electrodes 16 and ofthe constitution of the spin valve film 14.

The spin valve film 14 comprises a nonmagnetic underlayer 141 of Ta, Nb,Zr, Hf or the like having a thickness of from 1 to 10 nanometers, anoptional second underlayer 142 having a thickness of from 0.5 to 5nanometers, an antiferromagnetic layer 143, a pinned magnetic layer 144,an interlayer 145 having a thickness of from 0.5 to 4 nanometers, a freelayer 146, a second interlayer 148 having a thickness of from 0.5 to 4nanometers, a second pinned magnetic layer 149, a secondantiferromagnetic layer 150, and an optional protective layer 147 havinga thickness of from 0.5 to 10 nanometers.

At least one of the pinned magnetic layer 144 and the pinned magneticlayer 149 is a laminated, pinned magnetic layer, which comprises aferromagnetic layer A, an antiferromagnetically coupling layer and aferromagnetic layer B as in FIG. 17. In this, employable is any of 1) acombination of an SyAF-type pinned magnetic layer for the pinnedmagnetic layer 149 and a conventional, single-layered pinned magneticlayer for the pinned magnetic layer 144, 2) contrary to 1), acombination of an SyAF-type pinned magnetic layer for the pinnedmagnetic layer 144 and a conventional, single-layered pinned magneticlayer for the pinned magnetic layer 149, or 3) a combination ofSyAF-type pinned magnetic layers for both the pinned magnetic layer 149and the pinned magnetic layer 144.

The longitudinal bias layers 15 have a so-called abutted junction typedevice structure. These maybe formed according to a lift-off method,like in FIG. 17, FIG. 27 and FIG. 28. Briefly, the track edges of thespin valve film are etched away via a photo-resist mask, and thereafterthe longitudinal bias layers 15 are formed through sputtering, vapordeposition, ion beaming or the like. In this process, the etchingremoval of the spin valve film 14 is preferably so effected that atleast the conductor layer part of the spin valve film 14 is left as itis without being removed. For example, when the antiferromagnetic layer143 is of a γ-Mn-based alloy such as IrMn, it is desirable that at leasta part of the antiferromagnetic layer 143 is left as it is.

If the conductor part is left in the track edges, the contact resistanceof the abutted junction structure is lowered, and therefore theresistance of the spin valve device 13 could be lowered with ease. Withthe low-resistance spin valve device 13, heads could have highresistance to static electricity. Needless-to-say, the spin valve filmat the track edges may be completely etched away with no problem to formthe longitudinal bias layers.

The electrodes 16 may be formed along with the longitudinal bias layersin one and the same lift-off method. In this case, the spacing betweenthe electrodes is nearly the same as that between the longitudinal biaslayers. Alternatively, the formation of the electrodes may be effectedseparately from that of the longitudinal bias layers to form a so-calledlead-overlaid structure in which the spacing between the electrodes isnarrower than that between the longitudinal bias layers. The merit ofthe lead-overlaid structure is that, especially when the longitudinalbias layers are hard magnetic layers, the influence of the straymagnetic field from the hard magnetic layer could be trapped in thevicinity around the track edges in which the electrodes and the spinvalve film are laminated, whereby the sensitivity profile of thereproduction track width (this is defined by the electrode spacing) inthe track width direction could be sharper and its accuracy could beaugmented. In particular, for high-density recording for which thereproduction track width shall be of a sub-micron level, the merit ofthe structure is more remarkable than in the prior art technique.Naturally, the lead-overlaid structure could apply to the embodiments ofFIG. 21 and FIG. 27.

Fifth Embodiment

FIG. 30 shows still another embodiment of the invention. Like in thesecond embodiment shown in FIG. 21, a lower shield and a lower cap (notshown) are formed on a substrate (not shown), a spin valve film 13 isformed thereover, and an upper cap, an upper shield and a recording part(all not shown) are formed still thereover. At the both track edges ofthe spin valve film 13, formed are a pair of longitudinal bias layers 15and a pair of electrodes 16. One example of the longitudinal bias layersis illustrated, which is a laminate film comprising a underlayer 153, aferromagnetic film 151 and an antiferromagnetic film 152. Naturally, thelongitudinal bias layers may be of a hard magnetic film of CoPt or thelike.

The electrodes 16 are formed of a material at least containing alow-resistance metal, such as Ta/Au/Ta or the like. In the illustratedcase, the electrode spacing LD is narrower than the longitudinal biaslayer spacing HMD, and the spin valve film 13 and the electrodes 16 havea region in which they are face-to-face contacted, in the vicinity ofthe both track edges. The longitudinal bias layers and the electrodesare generally formed in a lift-off method, but they may be also formedthrough ion milling, reactive ion etching or the like. Thoughcomplicated, a dry process is suitable for forming precision electrodes.

In the region of the spin valve film 13 just below the electrodes 16where the longitudinal bias layers 15 do not exist, when the resistanceof the electrodes is much smaller than that of the spin valve film, forexample, when the former is at most 1/10 of the latter, then thereproduction sensitivity is greatly lowered in the region except theelectrode spacing region, for example, in the region of the spin valvefilm just below the electrodes, if the magnetization of the free layer146 in the spin valve film is settled nearly in the track widthdirection when the ambient magnetic field is zero. In that condition,therefore, the reproduction track width could be defined by theelectrode spacing LD, whereby a steep reproduction sensitivity profilecould be realized at the track edges.

In addition, in the illustrated constitution, since the face-to-facecontact region for the spin valve film 13 and the electrodes 16 could bemuch larger than in an ordinary abutted junction type constitution, thecontact resistance between the electrodes and the spin valve film couldbe well minimized. With this, therefore, low-resistance spin valvedevices could be realized, and even low-noise, ESD-resistantmagnetoresistance effect heads could be realized.

For further narrowing the reproduction track width for the purpose ofincreasing the recording density in coming devices, the electrodespacing LD must be narrowed. On the other hand, however, if theelectrode spacing is too narrow, it will be difficult to much morereduce the width or the height of the device. Therefore, it is desirablethat HD is larger than LD for increasing the yield of heads. Concretely,regarding the height which will be a dimension-determinant factor inmachine working for the purpose of increasing the yield of heads in massproduction, the height must be at least around 0.5 μm or larger. Whenthe reproduction track width is narrowed to 0.5 μm or smaller, it isdesirable that HD is settled larger than LD. However, this will bringabout the following problems.

The first is that, since the resistance of the spin valve film regionfor reproduction is reduced, the reproduction output is reduced. Thisproblem could be overcome by increasing the sheet resistance of the spinvalve film. In an ordinary SyAF-type pinned layer, the thickness of thepinned layer is larger than a conventional, single-layered pinnedmagnetic layer. Therefore, increasing the sheet resistance of the spinvalve film having such an ordinary SyAF-type pinned layer is difficult.However, as in Table 14 and Table 15, since the sum total of thethicknesses of the pinned magnetic layer, the nonmagnetic spacer layerand the free layer is limited to at most 14 nanometers in the invention,both high sheet resistance of at least 16 Ω and high resistance changerate of at least 8% could be attained.

TABLE 14 Spin Valve Film Constitution: 5 nanometer Ta/2 nm Au/7 nmIrMn/ferromagnetic layer B/antiferromagnetically couplinglayer/ferromagnetic layer A/nonmagnetic spacer layer/free layer/Ta TotalThickness Thickness Thickness Thickness of of of of FerromagneticFerromagnetic Thickness Ferromagnetic Nonmagnetic Thickness Layer LayerB of Coupling Layer A spacer of Free to Free (nm) Layer (nm) (nm) layer(nm) Layer (nm) Layer (nm)   2 nmCoFe 0.9 nmRu   2 nmCoFe   2 nmCu 0.5nmCoFe/ 9.9 2.5 nmNiFe 1.5 nmCoFe 0.8 nmRu   2 nmCoFe   2 nmCu 0.5nmCoFe/ 10.8   4 nmNiFe 1.5 nmCoFe 0.9 nmRu   2 nmCoFe 2.5 nmCu   3nmCoFe 9.9   2 nmCoFe 0.9 nmRu   2 nmCoFe   2 nmCu   1 nmCo/ 12.9   5nmNiFe 1.5 nmCoFe 0.9 nmRu 1.5 nmCoFe   2 nmCu   1 nmCo/ 9.9   3 nmNiFe  2 nmCoFe 0.9 nmRu 2.5 nmCoFe   2 nmCu   3 nmCoFe 10.4   2 nmCoFe   1nmRu 2.5 nmCoFe 2.5 nmCu   1 nmCo/ 13   4 nmNiFe 2.2 nmCoFe 0.8 nmRu 2.5nmCoFe   2 nmCu   2 nmCoFe/ 14 4.5 nmNiFe   3 nmCoFe 0.9 nmRu   3 nmCoFe  3 nmCu   1 nmCoFe/ 17.8   7 nmNiFe   3 nmCoFe 0.9 nmRu   3 nmCoFe   3nmCu   3 nmCoFe/ 14.8   2 nmNiFe 2.5 nmCoFe 0.8 nmRu   3 nmCoFe 2.5 nmCu  1 nmCoFe/ 16.8   7 nmNiFe   3 nmCoFe 0.7 nmRu   3 nmCoFe   3 nmCu   5nmCoFe 14.7

TABLE 15 Spin Valve Film Constitution: 5 nanometer Ta/2 nm NiFe/7.5 nmPtMn/ferromagnetic layer B/antiferromagnetically couplinglayer/ferromagnetic layer A/nonmagnetic spacer layer/free layer/Ta TotalThickness Thickness Thickness Thickness of of of of FerromagneticFerromagnetic Thickness Ferromagnetic Nonmagnetic Thickness Layer LayerB of Coupling Layer A spacer of Free to Free (nm) Layer (nm) (nm) layer(nm) Layer (nm) Layer (nm) 2 nmCo 0.9 nmRu 2 nmCo 2.5 nmCu   1 nmCo/2nmNiFe 10.4 2 nmCo 0.9 nmRu 2 nmCo 2.5 nmCu 0.5 nmCo/ 9.9   2 nmNiFe 2nmCoFe 0.9 nmRu 2 nmCoFe 2.5 nmCu   1 nmCoFe/ 9.7   2 nmNiFe 2 nmCoFe0.9 nmRu 2 nmCoFe 2.5 nmCu   3 nmCoFe 10.4

In order to realize high resistance change rates in such ultra-thin spinvalve films, it is desirable that 1) the ferromagnetic layers A and B inthe pinned magnetic layer are of an alloy of CoFe, CoNi or CoFeNi havinga stable fcc phase, 2) even in the free layer, used is Co or an alloy ofCoFe, CoNi or CoFeNi at least in the vicinity of the interface betweenthe free layer and the nonmagnetic spacer layer, and 3) in theantiferromagnetic film, used is an antiferromagnetic layer containing anoble metal element, such as PtMn, PtPdMn, IrMn, RhMn, RhRuMn or thelike.

The second problem with HD larger than LD is the Barkhausen noise. In aconventional abutted junction type spin valve device in which theelectrode spacing is nearly the same as the longitudinal bias filmspacing HMD, HMD is smaller than HD whereby the free layer isrectangular, having a longer side in the HD direction, and themagnetization direction of the free layer is readily oriented in theheight direction in which the intensity of the antimagnetic field issmaller. As a result, a Barkhausen noise occurs in this. As opposed tothis, since side of the rectangular spin valve film in the invention islonger in the track width direction as HMD is larger than HD therein,the magnetization direction of the free layer is prevented from beingoriented in the height direction. As a result, removing the Barkhausennoise from the device of the invention is easy. For these reasons, theyield of heads comprising the device of the invention is high.

Concretely, cases of 1) HD=0.5 μm, LD=0.45 μm, HMD=1.3 μm, and 2) HD=0.4μm, LD=0.35 μm, HMD=0.8 μm much enjoy the effect of the invention.

In the constitution of FIG. 29, the pinned magnetic layer is disposedbetween the free layer and the substrate. The same mentioned hereinshall apply to other cases where the free layer is disposed between thesubstrate and the pinned magnetic layer.

Sixth Embodiment

FIG. 31 shows still another embodiment of the invention. A substrate, alower shield and a lower gap (all not shown) are formed, and a pair oflongitudinal bias layers 15 are formed thereon according to a lift-offmethod or to any other dry process of ion milling, reactive ion etchingor the like. In FIG. 29, one example of the longitudinal bias layers isshown, which is a laminate comprising a underlayer 153 suitable to anantiferromagnetic layer, an antiferromagnetic film 152 of IrMn, RhMn,CrMn or the like, and a ferromagnetic film 151 of CoFe, NiFe, Co or thelike, as in the second embodiment. To this case, any other types oflongitudinal bias layers such as those illustrated in the secondembodiment could apply.

A spin valve film 13 is formed over the structure formed in that manner.In the spin valve film 13, it is desirable that the free layer 143 isdisposed nearer to the substrate than the pinned magnetic layer so as tofacilitate the easy contact between the longitudinal bias layers 15 andthe free layer 143. This is for the purpose of more effectively applyingthe bias magnetic field from the longitudinal bias layers to the freelayer 143. It is also desirable that the thickness of the underlayers141 and 142 below the free layer 143 is 10 nanometers. This is also forthe purpose of more effectively applying the bias magnetic field fromthe longitudinal bias layers to the free layer 143. It is furtherdesirable that the face-to-face contact region between the spin valvefilm 13 and the longitudinal bias layers 15 is minimized as much aspossible to prevent the Barkhausen noise.

Above the spin valve film 13, formed are a pair of electrodes 16according to a lift-off method, an ion milling method or a reactive ionetching method. Though not shown, an upper gap, an upper shield and arecording part are formed over the film 13.

Like in the fifth embodiment, HD is larger than LD but is smaller thanHMD. With that constitution, reproducing heads suitable to narrow trackwidth could be fabricated at high yields. Since the total thickness ofthe pinned magnetic layer, the nonmagnetic spacer layer and the freelayer is at most 14 nanometers, the resistance of the spin valve film 13is increased and the reproduction output is increased. With thatconstitution, high-sensitivity magnetoresistance effect heads can beobtained.

Seventh Embodiment Improvement in Thermal Stability and MirrorReflectivity, and Reduction in Magnetostriction

From the viewpoint of improving the thermal stability and the mirrorreflectivity and of reducing the magnetostriction, the seventhembodiment of the invention is described below.

Prior to introducing this embodiment, the problems which we, theinventors have recognized in the process of achieving this embodimentare mentioned.

For practical use of high-performance spin valve films (hereinafterreferred to as SV films), we, the inventors have recognized variousproblems such as the following:

-   (1) Poor thermal stability (especially in initial annealing).-   (2) Insufficient MR ratio for much more increasing reproduction    sensitivity.-   (3) When the free layer is a single-layered CoFe alloy layer capable    of giving relatively large MR ratio, then its magnetostriction    control is impossible, and good soft magnetic characteristics could    not be obtained.

These problems with SV films are mentioned in detail hereunder.

-   (1) Thermal stability:

As the general constitution of SV films, known is a few nm NiFe/about 1nm Co or a few nm NiFe/about 1 nm CoFe. The SV film structure with sucha free layer includes;

-   (a) 5 nanometer Ta/10 nm NiFe/1 nm Co/3 nm Cu/2 nm CoFe/7 nm IrMn/5    nanometer Ta,-   (b) 5 nanometer Ta/2 nm Cu/3 nm CoFe/3 nm Cu/2 nm CoFe/7 nm IrMn/5    nanometer Ta.

After annealed at 250° C. for 4 hours or so, the MR ratio of those SVfilms decreases by about 20% or more in terms of the relative ratiobased on the as-deposited films. For example, the MR ratio in theas-deposited SV film (a) is 6.4%, but, after annealed at 250° C. for 3hours, the MR ratio therein is 4.7%. Thus, the reduction in the MR ratioafter the annealing is more than 20% in terms of the relative ratiobased on the as-deposited film. The annealing step is indispensable infabrication of heads. The MR ratio in the as deposited SV film (b) nothaving a free layer of NiFe is 8.1%, but, after annealed at 250° C. for3 hours, the MR ratio therein is 6.5%. Even in the film (b), thereduction in the MR ratio after the annealing is about 20% in terms ofthe relative ratio based on the as-deposited film. At present, known isno means of preventing the MR ratio reduction without sacrificing themagnetic characteristics, or that is, any measure for improving thethermal stability for the MR ratio in SV films is not known.

For magnetic heads for high-density recording, desired are SV films withhigher MR ratio. However, as mentioned above, the MR ratio in theconventional SV films in the as-deposited condition is greatly loweredin thermal annealing that is indispensable to fabrication of heads. Thisproblem must be solved by all means for developing MR heads forhigh-density recording on a level of 10 Gdpsi or more.

-   (2) Increase in MR ratio by specular reflection:

In order to attain high MR ratio, another important matter, in additionto the means how to keep the original MR ratio in the as-depositedcondition still after thermal treatment as discussed in the previous(1), is how to increase the peak value of the MR ratio or, even thoughthe as-deposited film could not have a full-potential MR ratio, how torealize a film capable of having good MR ratio after thermal treatment.

Regarding the GMR effect, the frequency of spin-dependent scatteringincreases with the increase in the number of laminated layers ofmagnetic layers/nonmagnetic layers in a laminate film within the rangenarrower than the mean free path of electrons, and the increase in thenumber of laminated layers in the film brings about large MR ratio inthe film. However, in the constitution of the GMR film that is actuallyused in practical heads, such as the constitution of SV films, thereexist only the units of pinned magnetic layer/nonmagnetic spacerlayer/free layer. In general, therefore, the thickness of the GMR filmincluding SV films is smaller than the mean free path of electrons,which is against the MR ratio increase to which the invention isdirected.

In order to overcome this problem as much as possible, the number of thelayers constituting the GMR film may be increased. One example of suchGMR film constitution known in the art is a dual-spin valve film (or asymmetry spin valve, hereinafter referred to as D-SV film) in which thepinned magnetic layer is of a two-layered film composed of upper andlower layers and the upper and lower layers are separated by a freelayer existing therebetween. This will be helpful in solving theproblem, but at least at present could not solve all problems withpracticable SV films. For example, in the D-SV film where the free layeris subbed with a nonmagnetic spacer layer, it is difficult to make thefree layer have completely satisfactory soft magnetic characteristicscharacteristics with respect to, for example, the anisotropy field Hkand the level of magnetostriction λ. In addition, where the two upperand lower pinned magnetic layers are used, it is desirable that the twoantiferromagnetic films for pinning the magnetization of those twolayers have the same blocking temperature. In fact, however, it isdifficult to make the lower antiferromagnetic film, which is positionedin the lower side, and the upper antiferromagnetic film, which ispositioned in the upper side via a nonmagnetic spacer layer and a freelayer, have the same characteristics. Therefore, from the viewpoint ofthe MR ratio, the D-SV film is preferred, but from the viewpoint ofpractical applications, it still has many problems to be solved.

Given that situation, improving the characteristics of the popular SVfilm having one antiferromagnetic film is being much investigated. Onemeans for the improvement is to incorporate mirror reflectivity into thefilm. This is to dispose a reflective film on one or both sides of thebasic unit of the GMR film of magnetic layer/nonmagnetic spacerlayer/magnetic layer, so that electrons are elastically reflected on thereflective film to thereby prolong the mean free path of electrons inthe basic unit of the GMR film.

On the upper and lower layers of the basic unit of the conventional GMRfilm, electrons are scattered non-elastically. In that unit, therefore,electrons could not move to the length of the mean free path intrinsicto them, and they could not enjoy the spin-dependent scattering over thethickness of the basic unit of the GMR film. As a result, the MR ratioin the film could not be increased to a desired degree. Contrary tothis, if the GMR structure has upper and lower layers with ideal surfacereflectivity, the basic unit of the GMR film could be apparentlyequivalent to the constitution of an infinite artificial lattice film,in which electrons could scatter spin-dependently to the lengthcomparable to their mean free path. As a result, the MR ratio in thisGMR constitution could increase. The reflective films to be disposedover the upper and lower magnetic layer on the nonmagnetic spacer layermay be or even may not be spin-dependent ones. Even the latterspin-independent reflective films could fully exhibit the intendedeffect.

The effect applies not only to ordinary SV film structures but also toD-SV film structures. However, the reflective films would be ineffectivein artificial lattice films which naturally comprises a numerous andunlimited number of layers and in which electrons are naturallyscattered in a spin-dependent manner to the length of their intrinsicmean free path. The specular reflection effect is greater in SV filmstructures comprising a small number of constituent layers.

Some SV films have heretofore been proposed, which positivelyincorporate the specular reflection noted above. The following areexamples of those SV films.

-   (c) Si substrate/5 nm NiO/2.5 nm Co/1.8 nm Cu/4 nm Co/1.8 nm Cu/2.5    nm Co/50 nm NiO,-   (d) Si substrate/50 nm NiO/2.5 nm Co/2 nm Cu/3 nm Co/0.4 nm Au    (Ref.; J. R. Jody et al., IEEE Mag. 33, No. 5, 3580 (1997)),-   (e) MgO substrate/10 nm Pt/5 nm Cu/5 nm NiFe/2.8 nm Cu/5 nm Co/1.2    nm Cu/3 nm Ag (Ref.; Y. Kawabu et al., Summary of Reports in Spring    Meeting in 1997, p. 142, by the Japan Metal Society),-   (f) Si substrate/200 nm Si₃N₄/20 nm Bi₂O₃/4 nm Au/4 nm NiFe/3.5 nm    Cu/4 nm CoFe (Ref.; D. Wang et al., IEEE Mag. 32, No. 5, 4278    (1996)).

In those SV film structures, the underlined parts are those consideredas specular reflection films.

In the SV film (c), the upper and lower specular reflection films are ofan oxide. Simply, it is considered that insulating oxides having a highpotential barrier are more effective than metals for electron wavereflection, as having higher mirror-reflectivity. In addition, since theNiO film is not only a reflective oxide film but also anantiferromagnetic film, it further acts to spin the magnetization of themagnetic layer adjacent to NiO. The above are D-SV films. It is believedthat even normal SV films, reversal SV films and others having asingle-layered antiferromagnetic film could enjoy the specularreflection on one side. However, these have some disadvantages and arenot practicable in the current stage.

First, NiO has low magnetic coupling force and its practicability islow. This is because, in a weak magnetic coupling field, themagnetization direction of the pinned magnetic layer is unstable owingto the stray magnetic field from the recording media, and the outputwill fluctuate. In addition, irrespective of Nio and any other oxidesfor a cap layer, the contact resistance between the lead electrodes andthe upper oxide layer is large. The increase in the contact resistanceis unfavorable, as often causing ESD (electrostatic discharge). Inaddition, where CoFe is used as the free layer, it is understood thatthe CoFe layer could not exhibit soft magnetic characteristics if notoriented in fcc(111) Where the free layer is positioned in the lowerside, a subbing oxide layer, if used, for the free layer shall not workwell as a buffer layer for fcc(111)-orientation buffer for CoFe. Withthat constitution, the SV film could not have soft magneticcharacteristics.

In the SV film (d), the underlayer of NiO is an antiferromagnetic filmadditionally acting for specular reflection, and the top Au layer is areflective film. Also in the SV film (e), the top Ag film is areflective film. In (e), the potential difference between the Ag filmand the film surface induces specular reflection. The reason why thenoble metal film of Au or Ag is effective as the surface reflective filmis not clear. One reason is written in the reference for (d), in whichthey say that, since the surface diffusion of noble metal films ishigher than that of transition metal films, the surface planarity ofnoble metal films is higher than that of transition metals, andtherefore noble metal films will be ready to exhibit surface reflection.

The reflective films of metals are superior to those of oxides, as theformer are free from the problem of contact resistance with leadelectrodes, which problem, however, is inevitable in the latter.However, the mirror reflectivity of noble metal films of Au or Ag isoften lost in practical devices. This is because, in practical MRdevices or MR heads, the SV film is rarely exposed outside but isusually covered with any other additional film.

For example, in shielded MR heads, an upper magnetic gap film of aluminaor the like is laminated on the SV film. As so written in the referencefor (d), the specular reflection is much influenced by the surface orinterface condition. Therefore, if any additional film is provided overthe surface of the specular reflection film, the mirror reflectivity ofthe film shall naturally be varied by the overlying additional film. Thefilm structure in which the MR characteristics of the SV film are variedby the additional film that overlies the SV film is problematic in itspractical applications.

In fact, it is reported that, when a Ta film which is generally used asa protective film is laminated on the surface of the Au film in an SVfilm, then the Au film loses its mirror reflectivity. Accordingly, SVfilms utilizing the mirror reflectivity on their surface often losetheir effect in device structures that are directed to practicalapplications, and are therefore not practicable.

The SV film (f) incorporates the Au film as the specular reflectionfilm, like in (d). In (f), however, the Au film does not exhibit thereflective effect on its surface, but induces the mirror-reflectiveeffect in the interface between the metal films. In this connection, itis understood that, when the Au film is directly formed on a substratein the absence of a suitable underlayer therebetween, it often grows inislands. In order to prevent this, a particular underlayer is providedbetween the Au film and the substrate in (f). Above the underlayer, thesmoothness of the Au film formed is enhanced as much as possible so asto ensure a sharp interface between the Au film and the overlying NiFefilm.

However, the underlayer in (f) is not practicable. Briefly, in producing(f), an Au film is formed on the subbing Bi₂O₃ film having a thicknessof 20 nanometers. This is to utilize the fact that the Au film formed onthe subbing Bi₂O₃ film exhibits good reflectivity after it is annealedat 350° C. (Ref.; C. R. Tellier and A. J. Tosser, Size Ellects in ThinFilms, Chapter I, Elsevier, 1982; L. I. Maissel et al., Handbook of ThinFilm Technology, McGraw-Hill Publishing Company, 1983).

In addition, another underlayer of Si₃N₄ film having a thickness of 200nanometers is provided below the Bi₂O₃ film. In other words, thetwo-layered underlayer having a total thickness of 220 nanometers isformed below the Au film, which is then annealed at a high temperatureof 350° C. The thick underlayer having a thickness of 220 nanometers isextremely disadvantageous for narrow gaps that shall be much morenarrowed for the coming, high-density recording systems, and will bealmost impracticable. In addition, the high-temperature thermaltreatment at 350° C. will cause interfacial diffusion at the interfaceof magnetic layer/nonmagnetic spacer layer, thereby disturbing thespin-dependent scattering of electrons which is intrinsic andindispensable to GMR films. As a result, the MR ratio in the film willbe greatly lowered. The thermal treatment temperature for the film (f)will cause interfacial scattering even in other SV films thatincorporate a laminate film of Co (CoFe)/Cu/Cu(CoFe) having good thermalstability.

-   (3) Magnetostriction control in CoFe:

Where a CoFe layer is used as a free layer, it is understood that an fcc(111)-oriented underlayer may be applied thereto so as to inducefcc(111) orientation of the CoFe layer, whereby the soft magneticcharacteristics of the CoFe layer is improved. As the fcc(111)-orientedunderlayer, used is a Cu layer or an Au layer. However, we, theinventors have found that, in the conventional technique, themagnetostriction which is another important factor of soft magneticcharacteristics is not controlled at all, and that the thermal stabilityof the CoFe layer much depends on the underlayer. For example, the SVfilms based on the published patent specification noted above includethe following:

-   (g) 5 nanometer Ta/2 nm Cu/2 nm CoFe/3 nm Cu/2 nm CoFe/7 nm IrMn/5    nanometer Ta,-   (h) 5 nanometer Ta/2 nm Au/3 nm CoFe/3 nm Cu/2 nm CoFe/7 nm IrMn/5    nanometer Ta.

In the film (g), the Cu layer is oriented in fcc(111), and the CoFelayer above the fcc(111)-oriented Cu layer is also oriented in fcc(111)to exhibit soft magnetic characteristics. However, the film (g) isproblematic in that (i) its thermal stability is poor (the MR ratio inthe as-deposited film of 8.1% is decreased to 6.5% after thermaltreatment at 250° C. for 4 hours, and the MR ratio reduction in theheat-treated film is 20% in terms of the relative ratio), and (ii) themagnetostriction λ is −14×10⁻⁷, and its peak value is large. Thus, thefilm (g) is not always practicable. Regarding the magnetostriction λ,there is no definite standard in the art. As one standard, the preferredrange of the magnetostriction λ will fall between −10×10⁻⁷ and +10×10⁻⁷or so.

In addition, even when Au is used as the fcc material in place of Cu (asin the film (h)), the film is still problematic in that (i) its thermalstability is poor (the MR ratio in the as-deposited film of 8.4% isdecreased to 6.5% after thermal treatment at 250° C. for 4 hours, andthe MR ratio reduction in the heat-treated film is 23% in terms of therelative ratio), and (ii) the magnetostriction λ is +33×10⁻⁷ and itspeak value is large. Thus, like that with a Cu layer, the film is stillnot always practicable.

XRD patterns of the spin valve films (g) and (h) are obtained throughθ-2θ scanning, and studied. In those patterns, the three layers ofCoFe/Cu/CoFe had nearly the same d spacing value and gave one peak. Thisone peak is referred to herein. The fcc-oriented d-(111) spacing in thethree layers CoFe/Cu/CoFe above Cu is 2.054 nanometers; and thefcc-oriented d-(111) spacing in the three layers CoFe/Cu/CoFe above Auis 2.086 nanometers. As will be mentioned hereunder, at the intermediateof the d-(111) spacing above Cu and Au, the magnetostriction in thefilms could be suitably controlled and reduced. Therefore, it has beenfound that the too small d-(111) spacing above Cu and the too larged-(111) spacing above Au are both unfavorable.

As mentioned above, it has been found that forming the free layer ofCoFe on the merely fcc(111)-oriented underlayer is unsatisfactory inpoint of magnetostriction control. For reducing the magnetostriction,employable is a structure where CoFe is formed on an fcc(111)-orientedNi₈₀Fe₂₀ at around zero magnetostriction level so that the entire freelayer is made to have zero magnetostriction owing to that NiFe havingnearly zero magnetostriction (e.g., the constitution (a) noted above)However, as so mentioned hereinabove, this structure is stillproblematic in that its MR characteristic is still degraded in thermaltreatment.

As mentioned above, the MR ratio reduction in conventional spin valvefilms after thermal treatment is great, and the improvement in thethermal stability of the films is desired.

As one measure for increasing the MR ratio in spin valve films, specularreflection is widely noticed. However, the reflective film inconventional spin valve films is of an insulating material such asoxides, etc. In addition, some conventional spin valve films utilize thereflectivity on their surface. Therefore, the conventional spin valvefilms of those types often induce ESD, for example, owing to theincrease in the contact resistance with lead electrodes, or protectivefilms, if formed on the spin valve films, cancel the mirror reflectivityof the films. Thus, the conventional spin valve films have such variousproblems in their practical applications. Apart from those, anothertechnique of utilizing interfacial specular reflection is beinginvestigated. However, this requires a specific underlayer. Therefore,spin valve films utilizing such interfacial specular reflection arepoorly practicable. For these reasons and in consideration of thepractical applicability of spin valve films to devices and magneticheads, it is desirable that the MR ratio in spin valve films isincreased by specular reflection.

In addition, for improving the soft magnetic characteristics of spinvalve films, it is desired to control and reduce the magnetostriction inCo-based magnetic layers of CoFe alloys or the like.

In particular, the mirror reflectivity of spin valve films to increasethe MR ratio in the films and to reduce the magnetostriction thereinmust not be degraded in thermal treatment for ensuring the practicalapplication of the films.

This embodiment of the invention is to solve the problems noted above,and its object is to provide a magnetoresistance effect device in whichthe MR characteristic of the spin valve film is prevented from beingdegraded in thermal treatment, and to provide a magnetoresistance effectdevice in which the MR ratio in the spin valve film is increased byspecular reflection in consideration of its practical applications, inwhich the magnetostriction in the spin valve film is reduced, and inwhich the MR ratio reduction and the magnetostriction increase in thespin valve film in thermal treatment are both retarded. Another objectis to provide a magnetic head and a magnetic recording/reproducingsystem incorporating the magnetoresistance effect device and thereforehaving improved recording/reproducing characteristics and improvedpractical applicability.

The embodiment to solve the problems noted above is described below withreference to the accompanying drawings.

FIG. 32 is a sectional view of the essential structure of one embodimentof the magnetoresistance effect device (MR device) of the invention. InFIG. 32, 1 is a first magnetic layer, and 2 is a second magnetic layer.These first and second magnetic layers 1 and 2 are laminated via anonmagnetic spacer layer 3 existing therebetween. These first and secondmagnetic layers 1 and 2 are not antiferromagnetically coupled to eachother, but form a non-coupled, laminated magnetic film.

The first and second magnetic layers 1 and 2 may be made of aCo-containing ferromagnetic material of, for example, simple Co or a Coalloy. The magnetic layers 1 and 2 may also be made of an NiFe alloy orthe like. Of those materials, especially preferred is a Co alloy asbeing able to enlarge both the bulk effect and the interfacial effect,whereby the MR ratio in the MR device could be enlarged.

The Co alloy for constituting the magnetic layers 1 and 2 includesCo-based alloys containing at least one or more elements selected fromFe, Ni, Au, Ag, Cu, Pd, Pt, Ir, Rh, Ru, Os, Hf, etc. It is desirablethat the additive element content of the alloys falls between 5 and 50at. %, more preferably between 8 and 20 at. %. This is because, if theadditive element content is too small, the bulk effect of the alloyswill be poor; but, on the contrary, if the additive element content istoo large, the interfacial effect of the alloys will lower. Of theadditive elements, especially preferred is Fe, as giving large MR ratio.

Of the first and second magnetic layers 1 and 2, the lower firstmagnetic layer 1 is formed on a magnetoresistance effect-improving layer(MR-improving layer) 4. The MR-improving layer 4 is formed on anonmagnetic layer having a subbing function (hereinafter referred to asnonmagnetic underlayer) 5. The nonmagnetic underlayer 5 is, for example,a layer containing at least one element selected from Ta, Ti, Zr, W, Cr,Nb, Mo, Hf and Al, for which are used any of simple metals or alloys ofthose metals, or compounds such as oxides or nitrides of those metals.Where the nonmagnetic underlayer 5 is of an oxide of Ta or the like,electrons that could not be reflected on the MR-improving layer 4 couldbe reflected on the interface of nonmagnetic underlayer 5/MR-improvinglayer 4, as will be described in detail hereunder.

The first magnetic layer 1 is a free layer of which the magnetizationdirection varies depending an applied magnetic field. On the secondmagnetic layer 2, formed is an antiferromagnetic layer 6 of any of IrMn,NiMn, PtMn, FeMn, RuRhMn, PdPtMn or the like. From the antiferromagneticlayer 6, a bias magnetic field is applied to the second magnetic layer2, by which the magnetization of the layer 2 is pinned. Accordingly, thesecond magnetic layer 2 is a pinned magnetic layer.

Apart from the method of pinning the second magnetic layer noted abovein which the second magnetic layer is directly contacted with theantiferromagnetic layer for thereby pinning its magnetization direction,a so-called Synthetic antiferromagnetic structure may also be employedfor the intended pinning, though not shown in FIG. 32. Briefly, a thirdmagnetic layer is laminated on the second magnetic layer via a layer ofRu, Cr or the like, and the second magnetic layer and the third magneticlayer are antiferromagnetically coupled to each other in a manner ofRKKY. Using the Synthetic antiferromagnetic structure is preferred, asthe bias point is stabilized and the stability of the pinningcharacteristic at high temperatures is enhanced. Concretely, examples ofthe structure comprising the second magnetic layer and the thirdmagnetic layer include CoFe/Ru/CoFe, Co/Ru/Co, CoFe/Cr/CoFe, Co/Cr/Co,etc. The antiferromagnetic layers to be applied to the Syntheticantiferromagnetic structure may be the same as those mentioned above.

Examples of the material that constitutes the nonmagnetic layer 3 to bedisposed between the first and second magnetic layers 1 and 2 includeCu, Au, Ag and their alloys; paramagnetic alloys comprising any of thesemetals and magnetic elements; and Pd, Pt and alloys consistingessentially of these.

On the antiferromagnetic layer 6, formed is a protective layer 7. Theprotective layer 7 may be made of metals or alloys which are the same asthose for the nonmagnetic underlayer 5. These constituent layers formthe spin valve film 8 of this embodiment. A pair of electrodes (notshown) for supplying sense current are connected to the spin valve film8 to construct a spin valve GMR device. The spin valve GMR device may beprovided with a bias magnetic field-applying film of a hard magneticfilm or an antiferromagnetic film, which is to apply a bias magneticfield to the free layer. In this case, it is desirable that the biasmagnetic field is applied in the direction nearly perpendicular to themagnetization direction of the pinned magnetic layer 2. In FIG. 32, 9 isa substrate.

Of the layers constituting the spin valve film 8 noted above, theMR-improving layer 4 is the characteristic part of the invention. TheMR-improving layer 4 in FIG. 32 is of a laminate film comprising a firstmetal film 4 a and a second metal film 4 b. The metal films 4 a and 4 bfunction as underlayers for the spin valve film 8, and these may containat least one element selected from Cu, Au, Ag, Pt, Rh, Ru, Al, Ti, Zr,Hf. Pd and Ir.

Of those plural metal films, the essential element constituting thefirst metal film 4 a that is adjacent to the first magnetic layer (freelayer) 1 does not form solid solution with the essential elementconstituting the free layer 1. Preferably, the same shall apply also tothe second metal film 4 b. Specifically, it is desirable that theessential element constituting the second metal film 4 b does not formsolid solution with the essential element constituting the free layer 1.In particular, the essential elements each constituting those first andsecond metal films 4 a and 4 b may not form solid solution with eachother. It is further desirable that the first metal film 4 a to beadjacent to the free layer 1 is of a metal having a short electronwavelength, while the second metal film 4 b adjacent to the first metalfilm 4 a is of a metal having a longer electron wavelength (than that ofthe metal constituting the first metal film 1 a).

The definition “not forming solid solution” as referred to herein isexplained. For two different elements A and B, the condition in whichone element A does not form solid solution with another element B (forthe terminology “not forming solid solution”) is meant to indicate thefollowing condition: In a binary phase diagram (for example, see BinaryAlloy Phase Diagram, 2nd edition, ASM International, 1990, etc.), whenthe amount by at. % of B capable of dissolving in a matrix of A to formsolid solution at low temperatures around room temperature or so, andthe amount by at. % of A capable of dissolving in a matrix B to formsolid solution at such low temperatures are both at most 10%, thecombination of those elements A and B is in the condition of “notforming solid solution”.

Concretely mentioned are a case where the magnetic layer (for example,the free layer 1) is of Co or a Co alloy, and a case where the magneticlayer is of an Ni alloy. Since the subbing film is preferably of an fccmetal or an hcp metal for attaining the fcc orientation in the magneticlayer, the element constituting the MR-improving layer that is adjacentto the magnetic layer will be selected from Al, Ti, Cu, Zr, Ru, Rh, Pd,Ag, Hf, Ir, Pt, Au, etc. Of those elements, three elements of Cu, Ag andAu satisfy the requirement of not forming solid solution with Co. On theother hand, three elements of Ru, Ag and Au satisfy the requirement ofnot forming solid solution with Ni. For the magnetic layer of an Nialloy, Cu will form solid solution with the Ni alloy from the relationof the two, Cu and Ni in the phase diagram. However, the presentinventors experiments have revealed the fact that, when Cu is used inthe MR-improving layer, it forms less solid solution with Ni in theneighboring magnetic layer. Specifically, on the basis of theexperimental data mentioned below, it is decided that an Ni alloy and Cudo not form solid solution with each other.

When the free layer is thin, the MR-improving layer acts as thenonmagnetic high-conductivity layer in the first embodiment mentionedhereinabove. However, once the interface between the nonmagnetichigh-conductivity layer and the free layer has become diffusive owing toelectron diffusion in that interface, the electron transmittance fromthe free layer to the nonmagnetic high-conductivity layer is lowered. Inother words, even when the magnetization direction of the pinned layeris parallel to that of the free layer, the diffusive interface receivesnon-elastic electron scattering so that the mean free path of electronsfor up-spin could not be prolonged. As a result, this induces MR ratiodepression. This phenomenon is seen when the ultra-thin free layer formssolid solution with the nonmagnetic high-conductivity layer, and becomesmore remarkable in thermal treatment. Accordingly, the MR ratiodecreases after thermal treatment. To confirm this phenomenon, we, thepresent inventors made one experiment in which Cu is attached to an Nialloy layer. In that experiment, less MR ratio depression was seen.

From the experimental results noted above, it is decided that Ni alloysdo not form solid solution with Cu. Accordingly, Cu could be in thegroup of elements not forming solid solution with Ni alloys. For thesereasons, in the invention, the group of elements not forming solidsolution with Ni alloys shall include Cu in addition to the elements tobe derived from the phase diagram. Concretely, the group includes Ru,Ag, Au and Cu. With any of those elements being disposed adjacent to themagnetic layer which does not form solid solution with any of thoseelements, the compositional steepness in the interface between themagnetic layer and the MR-improving layer is not lost in thermaltreatment and good specular reflection could be expected.

The premise in this case is that the magnetic layer is fcc-oriented,which, however, is not imitative. Needless-to-say, the magnetic layermay be non-oriented or may have a microcrystalline structure, and theMR-improving layer may be applied to the magnetic layer of that type.Concretely, the magnetic layer may be any of amorphous magnetic layersor microcrystalline-structured magnetic layers of CoFeB, CoZrNb or Cr towhich may be added any of Ti, Zr, Nb, Hf, Mo, Ta or the like.

In the invention, the MR-improving layer comprising the elements notedabove may be partly in the form of a laminate film with any other metalfilms or of an alloy film with any other elements for the purpose ofmore ensuring the d-spacing control in the layer and themicrocrystalline structure of the layer. The elements constituting themetal films to form the laminate film are desirably fcc metals and hcpmetals, including, for example, Al, Ti, Cu, Zr, Ru, Rh, Pd, Ag, Hf, Ir,Pt, Au, etc.

Where the MR-improving layer is of a laminate film, metals of the metalfilms constituting it and not to be adjacent to the magnetic layer maybe capable of forming solid solution with the metals of the other metalfilms to adjacent to the magnetic layer.

Examples of using a laminate film for the MR-improving layer 4 arementioned below. Where the magnetic layer 1 is of Co or a Co alloy andthe metal film 4 a is of Cu not forming solid solution with theelement(s) of the layer 1, it is possible that the metal film 4 bcomprises at least one element selected from Al, Au, Pt, Rh, Pd and Irall capable of forming solid solution with Cu. Where the metal film 4 ais of Ag, the metal film 4 b may comprise at least one selected from Pt,Pd and Au. Where the metal film 4 a is of Au, the metal film 4 b maycomprise at least one selected from Pt, Pd, Ag and Al. Where themagnetic layer 1 is of an Ni alloy and the metal film 4 a is of Ru notforming solid solution with the elements of the layer 1, it is possiblethat the metal film 4 b comprises at least one element selected from Rh,Ir and Pt all capable of forming solid solution with Ru. To Ag and Aufor the film 4 b, the same as above for the metal film 4 a of Cu couldapply.

Of the combinations noted above, it is desirable that the two elementsconstituting the MR-improving layer 4 could form solid solution to alevel of at least 10%. For example, preferred are combinations of Au—Cu,Ag—Pt, Au—Pd, Pt—Cu, Au—Ag, etc. Regarding the combination of the metalfilm 4 a and the metal film 4 b, however, it is not always necessarythat the two can form solid solution in some degree. For example,combinations of Cu—Ru, Cu—Ag and the like are also employable herein.The laminate film for the MR-improving layer 4 is not limited to onlythe two-layered laminate film composed of the first metal film 4 a andthe second metal film 4 b, but may be composed of three or more layers.

The MR-improving layer 4 is not limited to the laminate film composed ofthe first metal layer 4 a and the second metal layer 4 b. For example,as in FIG. 33, the MR-improving layer 4 may be an alloy layer 4 c thatcomprises elements not forming solid solution with the essentialcomponents constituting the magnetic layer 1. To the alloy layer 4 c inthis case, the same as above for the laminate film could apply.Concretely, for example, where the magnetic layer 1 is of Co or a Coalloy, the alloy layer 4 c comprises, as the essential constituentelement, at least one selected from three elements of Cu, Ag and Au.Where the magnetic layer 1 is of an Ni alloy, the alloy layer 4 ccomprises, as the essential constituent element, at least one selectedfrom four elements of Ru, Ag, Au and Cu.

The alloy layer 4 c may comprise at least one additional element inaddition to the essential constituent elements noted above. As theadditional elements, used are elements capable of forming solid solutionwith the essential constituent elements of the alloy layer 4 c so as toprevent phase separation in the layer 4 c. For example, when theessential constituent element of the alloy layer 4 c is Cu, the alloyfor the layer 4 c shall contain a noble metal, including, for example,Cu—Au, Cu—Pt, Cu—Rh, Cu—Pd, Cu—Ir, etc. When the essential constituentelement of the alloy layer 4 c is Ag, the alloy for the layer 4 c maybea noble metal alloy, including, for example, Ag—Pt, Ag—Pd, Ag—Au, etc.When the essential constituent element of the alloy 4 c is Au, the alloyfor the layer 4 c may also be a noble metal alloy, including, forexample, Au—Pt, Au—Pd, Au—Ag, Au—Al, etc.

Of the alloys noted above, it is desirable that the two elementsconstituting the alloy layer 4 c for the MR-improving layer 4 could formsolid solution to a level of at least 10%. For example, preferred arealloys of Au—Cu, Ag—Pt, Au—Pd, Au—Ag, etc. As mentioned above, varioustypes of morphology could apply to the MR-improving layer 4. Forexample, the MR-improving layer 4 may also be a laminate film composedof the metal film 4 a and the alloy layer 4 c, as in FIG. 34.

Where the free layer 1 is of a Co-based magnetic material, it isdesirable that the MR-improving layer 4 which acts as the underlayer forthe free layer 1 is of a metallic material having the same fcc-crystalstructure as the Co-based magnetic material has, or of an hcp-structuredmetallic material capable of readily orienting the overlying film infcc-orientation. In view of those points, Cu, Au, Ag, Pt, Rh, Pd, Al,Ti, Zr, Hf, Ir and their alloys such as those mentioned above arepreferable materials for constituting the MR-improving layer 4. Further,when the MR-improving layer 4 is of a laminate film or an alloy layer ofthose metals, it is effective for reducing the magnetostriction in thefree layer 1 of a Co-based magnetic material such as Co—Fe alloys, etc.,as will be described in detail hereunder.

It is desirable that the thickness of the MR-improving layer 4 is atleast 2 nanometers, in order that the layer 4 could have the function asa underlayer. However, if too thick, the layer 4 will increase the shuntcurrent flow to thereby reduce the MR ratio in the film 8. Therefore, itis desirable that the thickness of the MR-improving layer 4 is at most10 nanometers, more preferably at most 5 nanometers.

The MR-improving layer 4 has the function of improving the thermalstability of the spin valve film 8, the function as a specularreflection film (interfacial reflection film) in the spin valve film 8,the function of still keeping high MR ratio even if the free layer isthin, the function of reducing the magnetostriction in the free layer 1of a Co-based magnetic material, and the function of controlling themicrocrystalline structure of the spin valve film 8. Based on thosefunction, the MR-improving layer 4 improves the MR characteristics ofthe spin valve film 8. The functions of the MR-improving layer 4 aredescribed in detail hereunder.

First referred to is the process of thermal degradation of spin valvefilms. One reason for the thermal degradation of the MR characteristicsof spin valve films during annealing is that the specular reflection onthe sides of the magnetic layers 1 and 2 not contacted with thenonmagnetic spacer layer 3 will vary during annealing. FIG. 35A to FIG.35C show the reduction in the MR ratio in spin valve films after thermaltreatment. In those, IF_(S) indicates the interface with spin-dependentscattering thereon, and IF_(M) indicates with no spin-dependentscattering but with specular reflection scattering thereon. Precisely,FIG. 35A and FIG. 35B schematically show an ideal condition (thiscorresponds to the as-deposited condition); and FIG. 35C schematicallyshows the condition after annealing.

As in FIG. 35A and FIG. 35B, specular reflection scattering occurs onthe both sides of the three-layered laminate structure, free layer1/nonmagnetic spacer layer 2/pinned magnetic layer 3, of the basic unitof the spin valve GMR in the as-deposited condition (even though theinterface is between metal films). However, as in FIG. 35C, in thesystem that readily forms solid solution in a process of annealing,interfacial diffusion occurs, or that is, the interface becomesdiffusive to lower its mirror-reflectivity after annealing. As a result,it is considered that, in that system, the MR characteristics aredegraded in thermal treatment.

Few reports are found relating to the specular reflection on theinterface between metal films, and any positive proof of the specularreflection on that interface has not been well established as yet.However, as will be mentioned hereunder, even on the interface betweenmetal films with small potential difference therebetween, some idealspecular reflection will occur. For example, specular reflection occurson the interface of NiFe/CoFe in the as-deposited condition in whichmixing of the two is relatively small. However, after the system ofNiFe—CoFe is annealed, interfacial diffusion occurs readily on thatinterface of NiFe/CoFe where the components will form solid solution,whereby the compositional steepness in the interface will be lost. As aresult, it is considered that the MR ratio will lower in that systemafter thermal treatment.

Concretely, in a spin valve film incorporating a free layer of alaminate film of NiFe/CoFe, the specular reflection on the NiFe/CoFeinterface is lost in annealing. As a result, for example, the MR ratioof 7.3% in the as-deposited film is lowered to 5.8% after annealing at250° C. for 4 hours. One reason for this will be because the specularreflection coefficient at the NiFe/CoFe interface would be varied inannealing, whereby the MR ratio in the film would be also varied afterannealing.

In the prior art technology, the interfacial specular reflection has notbeen taken into consideration since the NiFe/CoFe interface is theinterface between metal films and since the two, NiFe and CoFe are innearly the same electron condition. In the as-deposited condition, theinterface could be uniform with relatively low-level mixing of elementsthereon, and therefore specular reflection will occur even on the metalfilm interface of that type. However, since the NiFe/CoFe system formssolid solution in its interface, the interface will readily diffuse andmix when annealed, whereby the compositional steepness in the interfacewill be lost and the specular reflection coefficient therein will becomesmall. As a result, the MR characteristics in the system will bedegraded. In a different aspect, this means that the MR ratio in theas-deposited film is larger by the degree of specular reflection thanthat in the annealed film.

When the free layer is thin and MR-improving layer is disposed to thefree layer, the MR-improving layer acts as the nonmagnetichigh-conductivity layer in the first embodiment mentioned hereinabove.However, once the interface between the nonmagnetic high-conductivitylayer and the free layer has become diffusive owing to atomic diffusionin that interface, the electron transmittance from the free layer to thenonmagnetic high-conductivity layer is lowered. In other words, evenwhen the magnetization direction of the pinned layer is parallel to thatof the free layer, the diffusive interface receives non-elastic electronscattering so that the mean free path of electrons for up-spin could notbe prolonged. As a result, this induces MR ratio depression. Thisphenomenon is seen when the ultra-thin free layer forms solid solutionwith the nonmagnetic high-conductivity layer, and becomes moreremarkable in thermal treatment. Accordingly, the MR ratio decreasesafter thermal treatment.

It is important to form a stable interface between the free layer andthe nonmagnetic high-conductivity layer, which does not interfere withthe up-spin transmission even after thermal treatment. Concretely, it isimportant that the material of the free layer does not form solidsolution with the material of the nonmagnetic high-conductivity layer.For example, when the magnetic layer is of a Co alloy, then thenonmagnetic high-conductivity layer may be any of Cu, Au, and.

In view of the above, as one means of really preventing the MRcharacteristic degradation, it is important to dispose a metal materialwhich does not form solid solution with the materials of the magneticlayers 1 and 2, at the both sides of the basic unit of the GMR film. Inaddition, for example, when a material of CoFe alloys and the like isused in forming the basic GMR unit, the insoluble metal material layerof that type must have an additional function as a seed layer capable oforienting the CoFe alloy layer in fcc(111) orientation. Therefore, it isunderstood that metal materials capable of readily orienting in fcc(111)orientation are preferred for the additional metal layers. Moreover,when the free layer is of a CoFe alloy, magnetostriction control in thelayer is also important.

Another factor of the MR characteristic degradation in spin valve filmsin annealing is the change in the microstructure of the films in thermaltreatment. The microstructure of spin valve films is one importantfactor for improving the thermal stability of the films. For this, themicrostructure of the films is desirably such that, in the basic GMRunit of free layer/nonmagnetic spacer layer/pinned magnetic layer, allinterposing interfaces and the both outer interfaces could be keptstable even after thermal annealing. This is because the interfacebetween free layer/nonmagnetic spacer layer and that between nonmagneticspacer layer/pinned magnetic layer are both important for ensuringstrong, spin-dependent interfacial scattering thereon, and because theboth outer interfaces of the two magnetic layers are also important forthermally stabilizing the spin-independent specular reflectionscattering thereon. Where the magnetic layers are of laminate films, theinterface between the constituent magnetic films, one being adjacent tothe nonmagnetic spacer layer while the other being adjacent to that one,shall be the specular reflection interface for spin-independentscattering thereon.

In order to realize the condition noted above, it is naturally desirablethat the materials for magnetic layer/nonmagnetic layer are so selectedthat the material of the magnetic layer does not form solid solutionwith that of the nonmagnetic layer (for example, CoFe/Cu, or Co/Cu). Onthe interface of that type, the two materials do not form solidsolution. Therefore, it is important to prevent atomic diffusion on theinterface of magnetic layer/nonmagnetic layer and on the outer interfaceof the magnetic layer not adjacent to the nonmagnetic spacer layer. Forthis, ideally, it is desirable that the crystals in the basic GMR unitmoiety are single crystals. (In this connection, in one example ofCoFe/Cu/CoFe, the constituent crystals do not differ so much in thelattice constant, and the crystal grains do not separately exist in eachlayer but form aggregated grains in the integrated constitution ofCoFe/Cu/CoFe.) In fact, however, in the spin valve film 8 as formed onan amorphous layer of, for example, alumina or the like, single crystalsare difficult to form.

Therefore, for practicable and realizable crystal structures, preferredare so-called pseudo-single-crystal film structures in which theintergranular boundaries, if any are not ordinary intergranularboundaries but are so-called sub-grain boundaries with little in-planeorientation gap. In the invention incorporating the MR-improving layer 4noted above, spin valve films having small angle tilt boundaries ofsub-grain boundaries are obtained and their reproducibility is high.Concretely, the spin valve films of the invention can be oriented infcc(111) orientation, and the in-plane shift of the crystal orientationin the intergranular boundaries in the films could be limited within 30degrees. The magnetoresistance effect characteristics of the spin valvefilms of the invention are greatly improved owing to the grain controlin the films The crystal structures of the films will be described indetail hereunder.

Where the magnetization of the spin valve film is pinned with anMn-based ferromagnetic layer, for example, as in CoFe/Cu/CoFe/IrMn, theMR characteristics of the film will be greatly degraded if Mn passesthrough the intergranular boundaries therein to penetrate through theCoFe layer and diffuses even into the Cu layer. Therefore, in theconstitution of CoFe/Cu/CoFe/IrMn or the like, it is desirable that Mnis prevented from passing through the intergranular boundaries todiffuse into the Cu layer. On the other hand, since the interface of themagnetic layer not adjacent to the nonmagnetic spacer layer shall be theinterface to induce specular reflection, the microstructure of the spinvalve film is preferably such that the interface of the magnetic layeris difficult to disorder. For this, it is important that the material ofthe layer positioned outside of the ferromagnetic layer does not formsolid solution with the essential constituent element of the magneticlayer.

In the case where the antiferromagnetic layer is of IrMn or the like inwhich the lattice spacing greatly differs from that in CoFe, significantlattice distortion occurs between the CoFe layer and the overlying IrMnlayer. If so, atomic dislocation will occur in the interface ofCoFe/IrMn to relieve the lattice distortion therein. For preventing suchan unfavorable interfacial phenomenon, for example, an additional layercapable of stabilizing the lattice spacing in IrMn may be disposed onthe IrMn layer. For the additional layer, for example, an fcc metalmaterial in which the lattice spacing is nearly on the same level as inIrMn may be laminated over the IrMn layer. With that constitution, thethermal stability of the spin valve film could be improved.

Where the MR-improving layer is provided below the antiferromagneticlayer as the underlayer for the antiferromagnetic layer, it will beeffective for controlling the lattice spacing in the antiferromagneticlayer and, in addition, for enhancing the pinning ability of theantiferromagnetic layer. Even to that case where the MR-improving layeris provided directly adjacent to the antiferromagnetic layer, not onlyordinary pinned structures in which the pinned layer is directlycontacted with the antiferromagnetic layer but also Syntheticantiferromagnetic structures with Ru, Cr and others such as thosementioned above are applicable. In the combined constitution with theantiferromagnetic layer, the antiferromagnetic layer and theMR-improving layer do not diffuse too much in thermal treatment.Therefore, it is desirable that the material of the MR-improving layerdoes not form solid solution with that of the antiferromagnetic layer,or, when an γ-Mn-based antiferromagnetic material such as IrMn, RuRhMnor the like is used for the antiferromagnetic layer, the MR-improvinglayer is of an fcc metal material or an hcp metal material so as tostably keep the crystal structure of the antiferromagnetic layer.

Based on various advantages of specular reflection on the interface ofmetal film/metal film and others mentioned above, the magnetoresistanceeffect device of the invention is intended to have improved MRcharacteristics, improved thermal stability and improvedmagnetization-pinning characteristics. For that device with specularreflection on the metal/metal interface therein, the following twopoints must be taken into consideration. First, since there is smallpotential difference in the metal/metal interface, the interface couldnot ensure large specular reflection if based on the conventional idea.Secondly, when the film thickness is increased to some degree in orderto ensure the specular reflection effect of the reflective film of ametal, the metal film will produce shunt current flows as having smallresistance, whereby the current to flow in the basic GMR unit willdecrease and the MR ratio in the device will be reduced.

It is believed that metal films are inferior to oxide films with respectto their reflectivity. Though inferior to oxide films, metal films couldstill have good reflectivity. From the viewpoint of industrialapplicability, metallic reflective films are superior to reflectivefilms of oxides. Based on this point, the invention has been hereincompleted.

FIG. 36 is a schematic view of a model of metal/metal interface withgood specular reflection thereon. In place of ordinary electronpotential models generally employed in the art, herein used is anextremely simplified model for wave theory for facilitating theunderstanding of the invention. As in FIG. 36, when an electron having apredetermined Fermi wavelength has reached a metal/metal interface, thenthe wavelength of the electron shall change. In that condition, when theFermi wavelength of the electron is shorter in one metal film, thereflective film p, than the other metal film neighboring on the film p,then the electron as reached the film p at an angle θ smaller than thecritical angle θc (θc>θ) shall be all the time completely reflected onthe film p. With the difference between the Fermi wavelength of anelectron in the reflective film p and that in the neighboring metal filmbeing larger, the critical angle θ_(c) for the electron shall be larger,and, as a result, the mean reflectivity p as averaged for all electronsthat participate in electroconductivity shall be larger.

FIG. 37A and FIG. 37B are graphs indicating the ratio of the Fermiwavelength, Λ(p), in the reflective film p to the Fermi wavelength,Λ(GMR), in a GMR film neighboring on the reflective film p, Λ(GMR)/Λ(p),versus the critical angle θc. As is known from FIGS. 37A and 37B, themetal/metal interface could reflect electrons thereon to a satisfactorydegree even though the electron wavelength difference is not sosignificant. Needless-to-say, it is believed that the electronwavelength is infinite on a reflective film of an insulating material,and the critical angle θc for electrons on the reflective insulator filmis large. However, even for metal/metal interface, electrons couldreflect on the interface to a satisfactory degree. FIG. 38 is a graph ofthe data of the critical angle θc at which Au(Ag)/Cu interface producesspecular reflection, as calculated from the Fermi wavelength at theinterface. As is known from FIG. 38, the interface of Au(Ag)/Cu wellproduces satisfactory specular reflection thereon.

From the above, it is understood that, for the reflective film withmetal/metal constitution, the important matters are that (1) the Fermiwavelength of electrons in one metal film is as long as possible and (2)the compositional steepness in the interface between the metal films ishigh. The Fermi wavelength is generally on the order of a few angstrom.Therefore, if the compositional steepness is lost owing to theinterfacial diffusion over that order, the wave reflection will vary,depending on the wavelength, whereby the electron transmissionprobability will increase. Therefore, it is important how to increasethe compositional steepness at the film interface and how to make theFermi wavelength vary to a great extent on that interface. However,regarding (1), the relationship between the Fermi wavelength and thespecular reflection is not as yet clarified, and the Fermi wavelength isdifficult to calculate. Therefore, it is not clear as to whether or notthe condition (1) is indispensable herein. Therefore, we, the presentinventors have herein decided that the condition (2) is indispensable tothe present invention.

For satisfying the condition (2), it is especially important that thedifferent metals in the metal/metal film constitution do not form solidsolution when combined. If in the metal/metal system, metalprecipitation occurs easily on the interface through annealing, it willmuch increase the compositional steepness in the interface to furtherfacilitate specular reflection on the interface. Since the Fermiwavelength of electrons is naturally on the order of a few angstroms, itis desirable that the compositional steepness in the metal/metalinterface is dull on that order. Regarding the point (1) noted above, itis desirable that a metal film with a shorter electron wavelength isdisposed on the outer side of the magnetic layer while another metalfilm with a longer electron wavelength is on the outer side of theprevious metal layer, for enhancing the reflectivity of the metal/metalfilm constitution.

From the above, for really ensuring the specular reflection on themetal/metal interface, it is understood that one practicable method ofmaterial selection for the metal/metal film constitution is to disposean MR-improving layer of a metal not forming solid solution with theelement of the magnetic layer, on one side of the magnetic layer that isopposite to the side of the spacer layer. In addition, it is desirableto dispose the first metal film 4 a with a shorter electron wavelength,for example, on the outer side of the free layer 1 and to dispose thesecond metal film 4 b with a longer electron wavelength on the outerside of the film 4 a.

Where an alloy film is used as the reflective film, its resistance isgenerally larger than that of pure metal films, if it does not form acompletely regular alloy. In other words, the electron wavelength of thealloy film is long. This is advantageous for reflective films and isfurther advantageous in that the constituent elements of the alloy donot form solid solution with the elements of the neighboring film. Themethod of forming the alloy film of that type is not limited to directformation of the alloy film. Alternatively, plural films of alloyingsystems may be formed through lamination, whereupon an alloy may beformed in the interface of the laminate. However, when the free layer isthin, it is desirable that the specific resistance of the MR-improvinglayer adjacent to the free layer is lower. (In this connection, when thefree layer is thin, the MR-improving layer acts as the nonmagnetichigh-conductivity layer in the first embodiment.) Therefore, in thatcase, it is rather undesirable to form the alloy layer directly on thefree layer.

For the reasons noted above, in the spin valve films 8 as illustrated inFIG. 32, FIG. 33 and FIG. 34, the MR-improving layer 4 acting as thereflective film is so disposed that the metal film (concretely, thefirst metal film 4 a) not forming solid solution with the magnetic layer(free layer 1) is adjacent to the magnetic layer (free layer 1); and theMR-improving layer 4 acting as the reflective film is of a laminate filmcomposed of a plurality of metal films 4 a and 4 b, or the MR-improvinglayer 4 is of the alloy layer 4 c. The materials for constituting theplural metal films 4 a and 4 b and the alloy layer 4 c are selected onthe basis of the knowledge noted above. Where the MR-improving layer 4is of a laminate film, it is desirable that the first metal film havinga shorter electron wavelength is disposed adjacent to the magnetic layer1 for specular reflection. However when the free layer thickness is thinenough to have spin-filter effect, MR-improving layer 4 is preferred tohave low resistivity. The knowledge noted above shall apply to the otherconstitutive conditions than this.

The MR ratio in the MR film based on the specular reflection, orspin-filter effect when the free layer thickness is thin, noted above,is still kept as such even after annealing. This is because, owing tothe appropriate material selection for the MR-improving layer 4 (in thatthe specifically-selected material of the layer 4 does not form solidsolution with the elements in the neighboring layers), the compositionalsteepness in the interface in the film could be still maintained as sucheven after annealing. In other words, the MR characteristics ofconventional spin valve films are degraded in annealing owing to theinterfacial diffusion or mixing, but the spin valve films of theinvention can still maintain their as-deposited MR characteristics evenafter annealing. Accordingly, the spin valve films 8 of the inventionhave good thermal stability.

In the prior art spin valve film (e) mentioned above, the Cu/Ag laminatefilm is to enhance the specular reflection on its interface. This isbecause the surface roughness of the single-layered Cu film is large,and the Ag film is laminated on the Cu film. The idea for the prior artfilm (e) is obviously different from that for the spin valve film of theinvention in which the specular reflection on the metal/metal interfaceis intended to be augmented. Specifically, the prior art technique isfor surface planarization, while the technique of the invention is forincreasing the compositional profile in the metal/metal interface.Obviously, therefore, the material to be laminated differs between theprior art technique and the technique of the invention.

The MR-improving layer which is effective for improving the thermalstability of the MR device acts not only as the mirror-reflective filmbut also acts for microcrystalline film structure control, as somentioned hereinabove, thereby contributing to the improvement in the MRcharacteristics of the spin valve films 8. The MR-improving layer is notlimited to be below the free layer 1. Even when disposed above theantiferromagnetic layer 6, as in FIG. 39 and FIG. 40 (MR-improving layer4B), the layer well exhibits its functions. In those cases, theMR-improving layer 4B does not directly participate in magnetostrictioncontrol in the free layer. The MR-improving layer 4B of a laminate filmcomposed of a plurality of metal layers 4 a and 4 b or of an alloy layer4 c (these 4 a, 4 b and 4 c are mentioned hereinabove) is disposed onthe antiferromagnetic layer 6 of IrMn or the like such as that mentionedabove, and this acts for stabilizing the lattice spacing in theantiferromagnetic layer. As a result, dislocation on the interface ofmagnetic layer 2/antiferromagnetic layer 6 is prevented, whereby thethermal stability of the spin valve films 8 is much more improved.

When the lattice spacing in the antiferromagnetic layer is suitablycontrolled by the MR-improving layer, the other magnetization pinningcharacteristics of the films 8 are also improved. More effectively forthe lattice spacing control, the MR-improving layer acts as theunderlayer for the antiferromagnetic layer. This is especially effectivein bottom type spin valve films or dual spin valve films. Even in thefilms of those types, the lattice spacing in the antiferromagnetic layercould be freely and appropriately controlled by the laminated fcc metalor hcp metal film or alloy film specifically incorporated therein,whereby the magnetization pinning characteristics of the films could beimproved (with respect to the magnetic coupling bias field and thethermal stability).

Where the MR-improving layer 4B of a laminate film composed of aplurality of metal films 4 a and 4 b is disposed on theantiferromagnetic layer 6, it is desirable that the second metal film 4b of a metal having small surface energy, such as Au or the like, isdisposed to be adjacent to the antiferromagnetic layer 6. This isbecause, if the second metal film 4 b of Au, Ag or the like is adjacentto the protective film 7 of Ta or the like, the constituent metal of Au,Ag or the like will diffuse into the protective film 7 to lower thethermal stability. Therefore, it is desirable that the first metal film4 a of Cu or the like is disposed adjacent to the protective film 7. TheMR-improving layer 4B above the antiferromagnetic layer 6 may be of alaminate film of first metal film 4 a/second metal film 4 b/first metalfilm 4 a.

As mentioned hereinabove, the MR-improving layer 4 a of a metalliclaminate film or an alloy layer is effective for reducing themagnetostriction in the free layer 1 of a Co-based magnetic materialsuch as Co, a CoFe alloy or the like. If the single-layered magneticlayer 1 of CoFe is subbed with only a underlayer of simple Cu, negativemagnetostriction in the layer 1 will be great over −1 ppm, since thelattice spacing in the layer 1 is too small. On the other hand, if thesingle-layered magnetic layer 1 of CoFe is subbed with only a underlayerof simple Au, positive magnetostriction in he layer 1 will be great over+1 ppm, since the lattice spacing in the layer 1 is too large.

As opposed to those, when the MR-improving layer 4 of a metalliclaminate film or alloy layer 4 c that comprises at least one elementselected from Cu, Au, Ag, Pt, Rh, Pd, Al, Ti, Zr, Hf and Ir is providedas the underlayer for the free layer 1 of a Co-based magnetic materialsuch as Co, a CoFe alloy or the like, the fcc(111) orientation in thelayer 1 can be improved, and, in addition, the lattice spacing in thelayer 1 can be controlled to fall within a range effective formagnetostriction reduction. For example, the d(111) lattice spacing inthe layer 1 can be controlled to fall between 0.2055 and 0.2085nanometers. It is desirable that, in the MR-improving layer 4 which actsas the underlayer below the free layer 1, fcc-d(111) is larger than0.2058 nanometers. The d-(111) lattice spacing control in the layer 4may be effected, for example, as follows: When the layer 4 is of alaminate film of Au—Cu, the ratio of the Au thickness to the Cuthickness is varied for the intended control. When the layer 4 is of analloy film of Au—Cu, the alloying compositional ratio of Au to Cu isvaried for the intended control.

Concretely, it is desirable that the composition of the Au—Cu alloy forthe layer 4 falls within a range of Au₂₅Cu₇₅ to Au₇₅Cu₂₅ (at. %). Wherethe layer 4 is of a laminate film of alloy layers and metal films, it isdesirable that it has an Au-richer composition in some degree, ascompared with the layer 4 of a single-layered Au—Cu alloy film. Forexample, the laminate film of the layer 4 may have a composition ofAu₂₅Cu₇₅ to Au₉₅Cu₅ (at. %).

In the spin valve films 8 of FIG. 32, FIG. 33 and FIG. 34, the freelayer 1 is positioned in the lower site. However, these are notimitative. The invention encompasses bottom type spin valve films 8 ordual element-type spin valve films 8 in which the free layer 1 ispositioned in the upper site, for example, as in FIG. 41 and FIG. 42. Inparticular, in those bottom type spin valve films and dual spin valvefilms, the effect of the MR-improving layer as the subbing film for theantiferromagnetic layer is significant.

The spin valve films 8 of FIG. 41 and FIG. 42 has a structure ofnonmagnetic underlayer 5/MR-improving layer 4/antiferromagnetic layer6/pinned magnetic layer 2/nonmagnetic spacer layer 3/free layer1/MR-improving layer 4/protective layer 7 as laminated in that order onthe substrate 9. In the embodiment of FIG. 41, the MR-improving layer isof an alloy layer 4 c. In the embodiment of FIG. 42, the MR-improvinglayer 4 is of a laminate film of a plurality of metal films 4 a and 4 b.As in FIG. 34, a laminate film of a metal film 4 a and an alloy layer 4c is also employable for the layer 4 in those embodiments.

Where the MR-improving layer 4 as disposed above the free layer 1 is ofa laminate film, as in FIG. 42, it is desirable that the first metallayer 4 a of Cu or the like is disposed adjacent to the protective layer7, like in the upper MR-improving layer 4 in FIG. 39. Therefore, in FIG.42, the MR-improving layer 4 above the free layer 1 is of a laminatefilm of first metal film 4 a/second metal film 4 b/first metal film 4 a.

In the bottom type spin valve films, the MR-improving layer which is theunderlayer for the antiferromagnetic layer acts for film growth control,thereby improving the thermal stability and the pinning characteristicsof the films through lattice spacing control and microstructure control,and those effects of the MR-improving layer differ from the effects ofthe free layer for magnetostriction control and for specular reflectionimprovement. Therefore, so far as they are produced under the conditionunder which the microstructure of the antiferromagnetic layer therein iskept good, the bottom type spin valve films of the invention could fullyexhibit their good capabilities only with the MR-improving layer beingdisposed adjacent to the free layer even in the absence of theMR-improving layer below the antiferromagnetic film or even when theantiferromagnetic layer is disposed above an ordinary buffer layer ofTa, Ti or the like as in the ordinary subbing constitution inconventional reverse structures.

In the bottom type spin valve films 8, where the MR-improving layer 4 asabove is disposed adjacent to the free layer 1, the compositionalsteepness in the interface between the free layer 1 and the MR-improvinglayer 4 is kept to give specular reflection thereon, whereby the MRcharacteristics of the films could be ensured. When the free layerthickness is thin and the compositional steepness in the interfacebetween the free layer and the MR-improving layer 4 is kept to give thespin-filter effect, whereby the MR characteristics of the films could beensured. In those, as so mentioned hereinabove, the MR ratio supportedby the specular reflection or by the spin-filter effect is still kepteven after annealing, and the films could have good thermal stability.

In the reverse structure-type spin valve films 8 mentioned above, at theinterface of free layer 1/MR-improving layer 4, and even at theinterface of first metal film 4 a/second metal film 4 b at the interfaceof second metal film 4 b/third metal film 4 a in the MR-improving layer4 (FIG. 42) reflect electrons. Therefore, the constitution of the films8 differs from that of the prior art film (e) noted above having a Cu/Aulaminate film in that the surface of the Ag film reflects electrons inthe latter. In addition, the present invention has solved the problemwith the prior art film (d) which loses the reflectivity when Ta islaminated on the surface of the Au film therein. This is because thepresent invention utilizes the specular reflection on the metal/metalinterface, which being characterized in that each film thickness isspecifically defined in consideration of the Fermi wavelength ofelectrons and that the components in the interface do not form solidsolution.

In the prior art constitution (d), Ta is laminated on an extremely thinAu layer, of which the thickness is only 0.4 nanometers and is nearlythe same as the Fermi wavelength, and Ta will form solid solution withAu. In this, therefore, it is obvious that, even when the Co—Auinterface could be reflective, its reflection is lost as a whole. If thethickness of the Au film therein is made larger than the Fermiwavelength, such a thick Au film could be reflective as being influencedlittle by the interfacial diffusion of Ta thereinto, but, on the otherhand, negative influences of shunt current flow on the Au film will beenlarged. In place of the Au/Ta interface as in the prior artconstitution, if a laminate film of Au/Cu/Ta in which the Cu layer doesnot form solid solution with Ta is used, the Au interface is notdisturbed in the laminate. In addition, if an ultra-thin Cu layer isinserted, for example, between the interface of CoFe and Au, long-termdiffusion of Au into the nonmagnetic spacer layer could be prevented,and, in addition, the reflectivity of the resulting laminate could beenhanced since the Cu layer having a short Fermi wavelength isinterposed between CoFe and Au.

In the embodiments mentioned above, the MR-improving layer is disposedadjacent to the free layer 1 or the antiferromagnetic layer 6. Differentfrom those, other embodiments where the MR-improving layer 4 is disposedinside the free layer 1 or inside the pinned magnetic layer 2, forexample, as in FIG. 43, could produce the same results as above.

In the spin valve film 8 of FIG. 43, the free layer 1 is composed of,for example, an NiFe layer 1 a and a CoFe layer 1 b, and theMR-improving layer 4 of a laminate film of a plurality of metal films 4a and 4 b is interposed between the layers 1 a and 1 b. In this, theNiFe layer 1 a and the CoFe layer 1 b are ferromagnetically coupled toeach other via the MR-improving layer 4 existing therebetween, and thoseplural layers are integrated and magnetically acts as the integratedfree layer 1. Where the MR-improving layer 4 is interposed in theinterface of NiFe layer 1 a/CoFe layer 1 b (in this case, the layer 4does not form solid solution with both the layers 1 a and 1 b in theinterface), the NiFe layer 1 a and the CoFe layer 1 b must be integratedto act as the integrated free layer 1. In this case, therefore, theMR-improving layer 4 to be interposed must be thin. The MR-improvinglayer may also be interposed in the pinned magnetic layer 2. In thiscase, two or more magnetic films constituting the pinned magnetic layer2 are ferromagnetically or antiferromagnetically coupled to each other.The mode of ferromagnetic or antiferromagnetic coupling in the layer 2shall be determined, depending on the material and the thickness of theMR-improving layer 4 to be interposed in the layer 2.

The magnetoresistance effect device of the embodiments mentionedhereinabove may be mounted on separated recording/reproducing magneticheads, as the reproduction device part, for example, as in FIG. 44 andFIG. 45. Not limited to magnetic heads, the magnetoresistance effectdevice of the invention is also applicable to other various magneticmemory systems such as magnetoresistance effect memories (MRAM), etc.

FIG. 44 and FIG. 45 show the structures of embodiments of a separatedrecording/reproducing magnetic head which incorporates themagnetoresistance effect device of the invention as the reproductiondevice part. These are sectional views of separatedrecording/reproducing magnetic heads as seen in the medium facingdirection.

In those drawings, 21 is a substrate with a layer of Al₂O₃, such asAl₂O₃TiC. On the main surface of the substrate 21, formed is a lowermagnetic shield layer 22 of a soft magnetic material which includes NiFealloys, FeSiAl alloys, amorphous CoZrNb alloys, etc. On the lowermagnetic shield layer 22, formed is a spin valve GMR film 24 via a lowerreproduction magnetic gap 23 of a nonmagnetic insulating material suchas A₂lO₃ or the like. As the spin valve GMR film 24, used is the spinvalve film 8 of any of the embodiments mentioned hereinabove.

In FIG. 44, the spin valve GMR film 24 is so etched that its profilecould have a desired track width. The etching is to remove the outerregion of the film 24 that oversteps the recording track width. At theboth outer edges of the spin valve GMR film 24, disposed are films 25which are to apply a bias magnetic field to the film 24. The pair ofbias magnetic field applying films 25 are in abutted junction to theedges of the spin valve GMR film 24.

On the pair of bias magnetic field applying films 25, formed are a pairof electrodes 26 of Cu, Au, Zr, Ta or the like. To the spin valve GMRfilm 24, supplied is sense current from the pair of electrodes 26. Thesespin valve GMR film 24, paired bias magnetic field applying films 25 andpaired electrodes 26 constitute a GMR reproduction device part 27. Asmentioned above, the GMR reproduction device part 27 has a so-calledabutted junction structure.

In FIG. 45, the pair of bias magnetic field applying films 25 which areto apply a bias magnetic field to the spin valve GMR film 24 arepreviously formed between the spin valve GMR film 24 and the lowerreproduction magnetic gap 23 in the region not for the track width. Thepair of bias magnetic field applying films 25 are separated by apredetermined space therebetween, and the layers of the part outside thereproduction track for the spin valve GMR film 24 are laminatedthereover. On the spin valve GMR film 24, the bias magnetic fieldapplying films 25 may be laminated only at its both edges, if desired.

On the spin valve GMR film 24, formed are the pair of electrodes 26. Thesubstantial reproduction track width of the spin valve GMR film 24 isdefined by the distance between the pair of electrodes 26. These spinvalve GMR film 24, paired bias magnetic field applying films and pairedelectrodes 26 constitute the GMR reproduction device part 27 having anoverlaid structure.

In FIG. 44 and FIG. 45, an upper reproduction magnetic gap 28 of anonmagnetic insulating material, which may be the same as that of thelower reproduction magnetic gap 23, is formed on the GMR reproductiondevice part 27. On the upper reproduction magnetic gap 28, formed is anupper magnetic shield layer 29 of a soft magnetic material which may bethe same as that of the magnetic shield layer 22. These constituentelements form a reproducing head, shield-type GMR head 30.

A recording head, thin-film magnetic head 31 is formed on theshield-type GMR head 30. The lower recording magnetic pole of thethin-film magnetic head 31 and the upper magnetic shield layer 29 formone and the same magnetic layer. In other words, the upper magneticshield layer 29 of the shield-type GMR head 30 acts also as the lowerrecording magnetic pole of the thin-film magnetic head 31. On the lowerrecording magnetic pole 29 acting also as the upper magnetic shieldlayer, formed are a recording magnetic pole gap 32 of a nonmagneticinsulating material such as Al₂O₃ or the like, and an upper recordingmagnetic pole 33 in that order. Behind the medium-facing site, formed isa recording coil (not shown) which is to apply a recording magneticfield to the lower recording magnetic pole 29 and to the upper recordingmagnetic pole 33.

The reproducing head, shield-type GMR head 30, and the recording head,thin-film magnetic head 31 constitute the separatedrecording/reproducing magnetic head. The separated recording/reproducingmagnetic head of that type is combined with a head slider, and mountedon a magnetic head assembly, for example, as in FIG. 46. The magnetichead assembly 60 of FIG. 46 is provided with, for example, an actuatorarm 61 having a bobbin part for holding a driving coil, and a suspension62 is connected to one end of the actuator arm 61.

To the tip of the suspension 62, fitted is a head slider 63 which isprovided with the separated recording/reproducing magnetic head of theembodiment mentioned above. The suspension 62 is provided with a lead 64which is for writing and reading signals, and the lead 64 iselectrically connected to each electrode in the separatedrecording/reproducing magnetic head as incorporated in the head slider63. In the drawing, 65 are electrode pads in the magnetic head assembly60.

The magnetic head assembly 60 of the illustrated type is mounted on amagnetic recording/reproducing system such as a magnetic disc system orthe like, for example, as in FIG. 47. FIG. 47 shows the outlinestructure of a magnetic disc system 50 incorporating a rotary actuator.

As illustrated, the magnetic disc 51 is fitted to a spindle 52, and isrotated by a motor (not shown) that responds to the control signal froma driving system control source (not shown). The magnetic head assembly60 is so mounted on the system 50 that the head slider 63 as fitted tothe tip of the suspension 62 could float above the magnetic disc 51 forthe intended information recording and reproduction. While the magneticdisc 51 is rotated, the medium-facing site (ABS) of the head slider 63is held above the magnetic disc 51 via a predetermined floating distance(from 0 to 100 nanometers).

The actuator arm 61 of the magnetic head assembly 60 is connected to avoice coil motor 51 which is one type of a linear motor. The voice coilmotor 53 comprises a driving coil (this is coiled in the bobbin part ofthe actuator arm 61 and is not shown herein) and a magnetic circuit. Themagnetic circuit comprises facing permanent magnets and facing yolks alldisposed to sandwich the driving coil therebetween. The actuator arm 61is held by ball bearings (not shown) as disposed in two sites, upper andlower sites of the fixed shaft 54, and is rotatable and slidable by thepower of the voice coil motor 53.

The above is to exemplify one embodiment of the invention for separatedrecording/reproducing magnetic heads. Not limited to only such heads,the magnetoresistance effect device of the invention is applicable toany other head structures, for example, to an integratedrecording/reproducing magnetic head that comprise one and the samemagnetic yolk for both the recording head and the reproducing head.Still not limited to only magnetic heads, the magnetoresistance effectdevice of the invention is further applicable to any other magneticmemory systems such as magnetoresistance effect memories (MRAM), etc.

The invention is described in more detail with reference to thefollowing Examples, in which the samples produced were tested andanalyzed for their characteristics.

EXAMPLE a

In Example a, produced was a spin valve film of 5 nanometer Ta/1 nm Au/1nm Cu/4 nm CoFe/2.5 nm Cu/2.5 nm CoFe/7 nm IrMn/5 nanometer Ta, in a DCmagnetron sputter. The vacuum degree in the sputter was at most 1×10⁻⁷Torr, in which the argon pressure was from 2 to 10 mTorr. In fabricatingmagnetic heads, the film is formed on the Al₂O₃ gap on an AlTiCsubstrate. It has been confirmed that the properties of the film do notvary.

The spin valve film had an MR ratio of 9.6% in the as-depositedcondition, but after having been annealed at 250° C. for 4 hours in amagnetic field of 5 kOe, its MR ratio was still 9.0%. Themagnetostriction in the film was on the order of at most ±10⁻⁶. Hk of afilm sample having been annealed in a magnetic field applied in thedirection of the easy axis is defined as saturation Hk of the filmsample. Hk of the film produced herein was about 8 Oe and was small.This support the soft magnetic characteristics of the film. Hc of thefilm in the easy axis direction fell between 0 and 3 Oe, and was small.

In the film, the laminate film of Au/Cu is the MR-improving layer. Inthe interface between Au and Cu, formed is their alloy. In the interfacebetween Cu and CoFe, formed is no solid solution. In the interfacebetween Ta and Au, formed is their solid solution. However, since thethickness of the laminate of Au/Cu is much longer than the electronwavelength, the electron reflection on the interface is satisfactory.Therefore, the solid solution interface existing in the film causes noproblem for electron reflection. In the presence of the fcc-structuredAu/Cu underlayer, the layer of CoFe was well oriented in fcc(111)orientation. In addition, the d(111) spacing in CoFe is 0.2074nanometers, and the magnetostriction therein was controlled to be small.

The cross section of the spin valve film of this Example 1 was observedthrough TEM (transmission electron microscopy) As a result, it wasconfirmed that the GMR basic unit moiety of CoFe/Cu/CoFe was formed onthe underlayer of Au/Cu in regular layer by layer, and was oriented infcc(111) orientation. In microdiffraction of the free layer, CoFe layerpart, the fcc-d(111) spacing was found 0.2074 nanometers. The spacing isfavorable to magnetostriction control. FIG. 48 shows the XRD pattern ofthe spin valve film. Through the X-ray diffraction of the film, thefcc-d(111) spacing in CoFe was found 0.2074 nanometers.

In the XRD profile in FIG. 48, the peaks 1, 2 and 3 are for IrMn, andthe peak 4 will be the fcc(111) peak for the laminate film ofCoFe/Cu/CoFe. The d-spacing in the free layer only is difficult todetermine. In this case, the d-spacing for the peak 4 is considered asthe d-spacing in the free layer.

In place of the underlayer of 1 nm Au/1 nm Cu, when a underlayer of 2 nmCu only was used, then the fcc-d(111) spacing in CoFe decreased to0.2054 nanometers and the magnetostriction increased in the negativeside. On the other hand, when a underlayer of 2 nm Au only was used,then the fcc-d(111) spacing in CoFe increased to 0.2086 nanometers andthe magnetostriction increased in the positive side. Only when theunderlayer of Au/Cu was used, the suitable spacing of 0.2074 nanometerswas realized.

The thermal stability of the prior art film (g) where the underlayer isof Cu is not good. However, the thermal stability of the film of thisExample where the underlayer is of a laminate film of Au/Cu is good. Onereason will be because of the difference in the lattice spacing betweenthe two which will have some influence on the magnetostriction of thefilms. Precisely, the lattice spacing is narrowed on the Cu underlayer,whereby the lattice unconformity in the interface to IrMn is augmentedand the distortion is enlarged. When the film with such large distortionis annealed, the distortion is relaxed whereby the interface between thepinned magnetic layer and the antiferromagnetic film becomes diffusive.This influence is larger when the IrMn layer is thicker. On the otherhand, the lattice spacing in the underlayer of Au/Cu is nearer to thatin IrMn. Therefore, the film of CoFe/Cu/CoFe to be laminated on theAu/Cu layer is, contrary to the case having the simple Cu underlayer, tohave a distorted lattice of which the lattice constant is near to thatof IrMn. As a result, the influence of annealing on the distortionrelaxation in the case having the laminate underlayer of Au/Cu will besmaller.

In the other prior art constitution (h) having an Au underlayer, thelattice spacing is larger, contrary to that in (g). In the case (h),therefore, the distortion energy of CoFe/Cu/CoFe is too large so thatthe interfacial dislocation occurs with ease. As a result, the film (h)is degraded in initial annealing. When the Au layer is directlylaminated on the CoFe layer, Au will diffuse even into the nonmagneticspacer layer of Cu while passing through the intergranular boundaries.If Au reaches the nonmagnetic spacer layer, the MR ratio in the filmimmediately decreases. The MR ratio reduction worsens the long-termthermal stability of the film. However, if the laminate film of Au/Cu isdisposed as the underlayer below CoFe, the Cu layer acts as a stopper toprevent Au diffusion, and the long-term thermal stability of the film isthereby stabilized.

The underlayer of Ta is a buffer layer necessary for two-dimensionalgrowth of Au. If Au is directly formed on amorphous Al₂O₃, it willisland-wise grow. In that condition, where the pinned magnetic layer andthe free layer are magnetically coupled to each other via the spacerlayer, Hin will increase. In producing practical devices, the films areformed on processed substrates. For the devices, therefore, the bufferlayer is indispensable for stable film formation. In this Example, Tawas used for the underlayer. Apart from this, any others of Ti, Zr, Cr,W, Hf, Nb, their alloys, and their oxides and nitrides are usable forthe underlayer.

In the prior art film (f), the underlayer below Au has a total thicknessof 220 nanometers. As opposed to this, in this Example, the Taunderlayer is enough to prevent island-like growth of Au and toplanarize the Au surface. The interface between Au and the overlyingCu/CoFe film is also planarized. In addition, the film of this Exampledoes not require high-temperature thermal treatment at 350° C. The bestthermal treatment to which the film of this Example is subjected is at270° C. and for 4 hours or so. In that thermal treatment, thecompositional steepness in the interlayer is kept best. For thesereasons, the nonmagnetic underlayer of Ta is important. When combinedwith any other ordinary underlayer, the Ta underlayer planarizes the Aufilm formed thereon.

When any of 5 nanometer Ti, 5 nm Zr, 5 nm W, 5 nm Cr, 5 nm V, 5 nm Nb, 5nm Mo, 5 nm Hf and their alloys (5 nanometer Thick) was used as thenonmagnetic underlayer, the same results as above were also obtained.When any of 0.5 to 2 nm Au/0.5 to 2 nm Cu, 0.3 to 1 nm Au/0.3 to 1 nmCu/0.3 to 1 nm Au/0.3 to 1 nm Cu, or 0.5 to 5 nm AuCu/0.5 to 2 nm Cu wasused as the MR-improving layer, the same results as above were alsoobtained.

The MR-improving layer may be of a two-layered or even moremulti-layered film, or a single-layered alloy film. However, when itdoes not contain an additive element capable of increasing resistanceand if its thickness is large, the shunt current flow will increase.Therefore, the thickness of the MR-improving layer is preferably at most5 nanometers. However, it must have an additional seed effect for fccorientation as the underlayer, it is desirable that the MR-improvinglayer to be disposed below the magnetic layer has a thickness of from 2to 5 nanometers or so.

Except the combination of Au—Cu, other examples of the laminate film andthe alloy layer that may be combined with the magnetic layer of aCo-based alloy include Ru—Cu, Au—Cu, Pt—Cu, Rh—Cu, Pd—Cu, Ir—Cu, Ag—Pt,Ag—Pd, Ag—Au, Au—Pt, Au—Pd, Au—Al, etc. In those combinations, theessential element in the MR-improving layer to be disposed adjacent tothe Co-based magnetic layer is any of Cu, Au and Ag.

Regarding the film constitution, any of two-layered laminates, such asAu—Cu, Ru—Cu illustrated herein, or three-layered or more multi-layeredlaminates, or even single-layered or multi-layered alloy films areemployable. Regarding the film thickness, the same as that for the filmof Au—Cu illustrated herein shall apply to those modifications. When thefilms do not contain a third element, their thickness is preferably from2 to 3 nanometers or so in terms of the total thickness.

Preferred combinations to be applied to the Co-based magnetic layer areAu—Cu, Ag—Pt, Au—Pd, Au—Ag, Pt—Cu and the like, as they ensuremicrostructure films and as they form solid solution with ease. Of thosecombinations, the best one ensuring good lattice constant control isdetermined.

Like in the case where the magnetic layer is of a Co-based material, thecombinations for the laminate films or alloy layers for the MR-improvinglayer to be disposed adjacent to the magnetic layer of an Ni-basedmaterial include Au—Pt, Au—Pd, Au—Ag, Au—Al, Ag—Pt, Ag—Pd, Ru—Rh, Ru—Ir,Ru—Pt, etc. In those combinations, the essential element in theMR-improving layer to be disposed adjacent to the Ni-based magneticlayer is any of Au, Ag and Ru. Regarding the film constitution and thefilm thickness, the same as that for the Co-based magnetic layer couldapply also to the case of the Ni-based magnetic layer.

The two elements constituting the MR-improving layer may be those notforming solid solution. For example, in the case of Co-based magneticlayer, the MR-improving layer may be of a laminate film of Cu—Ru orCu—Ag. Those combinations not forming solid solution are not suitablefor alloy layers. This is because alloy layers of those combinationswill readily give separated two phases. Therefore, those combinationsare preferably used for laminate films. Specific examples of theNi-based magnetic layer include NiFe, NiFeCr, NiFeNb, NiFeRh, etc.

Regarding the pinned magnetic layer constitution, the pinned magneticlayer is directly laminated on the antiferromagnetic layer in the caseillustrated herein. In place of the simple structure, also employableare Synthetic antiferromagnetic structures. For example, in place of 2.5nm CoFe/7 nm IrMn, employable are 3 nm CoFe/0.9 nm Ru/3 nm CoFe/7 nmIrMn, 3 nm CoFe/0.9 nm Cr/3 nm CoFe/7 nm IrMn, etc. The thickness of twopinned layer may be different each other.

The antiferromagnetic film may be of any material of PtMn, NiMn, RuRhMn,CrMn, FeMn, NiO, etc. The material of the pinned magnetic layer may beany of Co or NiFe.

The nonmagnetic underlayer is not limited to only metal films of Ta,etc. For example, oxide films of TaO_(x) or the like are alsoemployable. Using the underlayer of TaO_(x) in place of Ta gave the samegood results. In this case, electrons not reflected on the MR-improvinglayer could be reflected on the interface of TaO_(x)underlayer/MR-improving layer in which the potential difference islarge, whereby the MR ratio in the film was much more increased.However, if CoFe is formed directly on the underlayer of TaO_(x), itcould not be oriented in fcc(111) orientation or could not have asatisfactory fcc-d(111) spacing favorable to magnetostriction control.As opposed to the case, a underlayer of TaO_(x)/Au/Cu is good inpractical applications. In place of TaO_(x), also employable are otheroxides of Ti, Zr, Cr, W, Hf, Nb, etc. Further employable are nitridessuch as TiN, TaN.

EXAMPLE b

In this Example b, produced was a spin valve film of 5 nanometer Ta/1 nmAu/1 nm Cu/4 nm CoFe/2.5 nm Cu/2.5 nm CoFe/7 nm IrMn/0.5 nm Au/0.5 nmCu/5 nanometer Ta, in the same manner as in Example a.

The lattice constant of the Au/Cu laminate film, which is the upperMR-improving layer, is nearer to that of IrMn, than that of the laminatefilm of CoFe/Cu/CoFe. Therefore, forming the laminate of Au/Cu on IrMnstabilizes more the lattice constant of IrMn, whereby the thermalstability of the film is much more improved. Disposing the Au layerdirectly below the protective film of Ta gives a structure where the Aulayer having small surface energy is directly below the Ta layer havinglarge surface energy. In that structure, Au readily diffuses into Ta todegrade the thermal stability of the film. Therefore, disposing Au or Agdirectly below Ta is unfavorable. Like in this Example, it is desirablethat the Ta protective film is formed via the Cu layer. An alloy layerof AuCu gives the same good results.

EXAMPLE c

In this Example c, produced was a spin valve film of 5 nanometer Ta/5 nmNiFeCr/1 nm Au/1 nm Cu/3 nm CoFe/2.5 nm Cu/2.5 nm CoFe/7 nm IrMn/5nanometer Ta, in the same manner as in Example 1. In this spin valvefilm, the free layer is of a laminate film of 5 nm NiCoFe and 3 nm CoFeas separated by Au/Cu existing therebetween.

As one comparative case to this Example, prepared was a spin valve filmof 5 nanometer Ta/5 nm NiFeCr)/3 nm CoFe/2.5 nm Cu/2.5 rim CoFe/7 nmIrMn/5 nanometer Ta also in the same manner as above.

The comparative spin valve film had an MR ratio of 8.6% in theas-deposited condition, but after having been annealed at 250° C. for 4hours, its MR ratio lowered to 6.6%. The MR ratio reduction was 23%.This is because CoFe and NiFeCr form solid solution in this structure.In the as-deposited comparative film, the constituent elements are notmixed so much in the CoFe/NiFeCr interface and the film had a high MRratio. However, after annealed at 250° C. for 4 hours, the CoFe/NiFeCrinterface was readily disturbed. In this comparative case, added wasabout 4% of Cr to NiFe for current shunting in NiFeCr. The same resultswere also obtained in the case having Ni₈₁Fe₁₉ (at. %).

As opposed to the comparative case, interposing the Au/Cu laminate filmbetween CoFe and NiFeCr as in the case of this Example 3 prevents theelement diffusion in the interface therebetween. As a result, theas-deposited film of Example 3 had an MR ratio of 8.7%, and even afterannealed at 250° C. for 4 hours, the annealed film still had an MR ratioof 8.1%. This, in this film, the MR ratio reduction after annealing iswell retarded. One reason for this is that, owing to the diffusionpreventing effect of the interposed Au/Cu layer, the interfacialreflection on the CoFe layer was still kept good even after annealing.

In place of 1 nm Au/1 nm Cu, also employable is any of 0.5 nm Au/0.5 nmCu, 0.5 nm Cu/0.5 nm Au, 0.3 nm Au/0.3 nm Cu/0.3 nm Au, 0.3 nm Au/0.3 nmCu/0.3 nm Au/0.3 nm Cu, 0.5 nm AuCu/0.5 nm Cu, 1 nm AuCu/0.5 nm Cu, 0.5nm Ag/0.5 nm Cu, 0.5 um Cu/0.5 nm Ag, 0.3 nm Ag/0.3 nm Cu/0.3 nm Ag, 0.3nm Ag/0.3 nm Cu/0.3 nm Ag/0.3 nm Cu, 0.3 nm Pt/0.3 nm Cu, 0.5 nm Cu/0.5nm Pt, 0.5 nm Pt/0.5 nm Cu, 0.5 nm Pt, 0.5 nm Pt/0.5 nm Cu/0.5 nm Pt/0.5nm Cu, 0.5 to 1.5 nm AuCu, etc. Those gave the same good results asherein.

The reason why NiFeCr was used as the second magnetic layer herein is asfollows: Adding Cr to NiFe increases resistivity ρ, without drasticreducing Ms, whereby the shunt current is reduced. In order to preventthe increase in the magnetostriction, λ, in the positive site, which iscaused by the Cr addition, it is desirable that the ratio of Ni to Fe isshifted to the Ni-rich site in some degree from the ordinaryzero-magnetostriction composition of Ni:Fe=81:19. One preferredcomposition is Ni₈₁Fe₁₅Cr₄, which satisfactorily controls all Ms, ρ andmagnetostriction. Apart from this, also employable are Ni₈₀Fe₂₀, NiFeNb,NiFeRh, etc.

EXAMPLE d

In this Example d, produced was a spin valve film of 5 nanometer Ta/1 nmAu/1 nm Cu/7 nm IrMn/2.5 nm CoFe/2.5 nm Cu/4 nm CoFe/0.5 nm Cu/0.5 nmAu/0.5 n Cu/5 nanometer Ta, in the same manner as in Example a.

The film produced herein is a so-called bottom type spin valve film inwhich the pinned magnetic layer is below the nonmagnetic spacer layer.The upper Cu/Au/Cu layer is the MR-improving layer, by which the thermalstability of the film and also the MR ratio in the film are increased.The lower Au/Cu layer is the subbing film for IrMn, while additionallyacting as the MR-improving layer for stabilizing the lattice constant ofIrMn. The as-deposited film had an MR ratio of 10%, and after annealedat 250° C. for 4 hours, the annealed film had an MR ratio of 9.5%. TheCu/Au interface formed an alloy of AuCu.

The upper Ta in the film of this Example d is the protective film, andthis is not intended to be reflective. In this Example d, the Cu/Au/Culayer is the MR-improving layer. Therefore, in this, the CoFe/Auinterface and the Cu/Au interface (or the AuCu alloy layer) shall bereflective. Thus, the constitution of the film of this Example obviouslydiffers from the prior art constitution of (e) or (d) mentioned above.In addition, in this, the ultra-thin Cu layer is interposed in theCoFe/Au interface, by which long-term diffusion of Au into thenonmagnetic spacer layer of Cu is prevented. Moreover, in this, sincethe Au layer is disposed via the layer having a short Fermi wavelength,the interlayer reflection is much augmented.

In place of the MR-improving layer of 1 nm Au/1 nm Cu, also employableis any of 0.5 to 3 nm Au/0.5 to 3 nm Cu, 0.5 to 3 nm Cu/0.5 to 3 nmAu/0.5 nm Cu, 0.5 to 3 nm AuCu/0.5 to 3 nm Cu, 0.5 to 3 nm Cu/0.5 to 3nm AuCu/0.5 to 3 nm Cu, 0.5 to 3 nm Ag/0.5 to 3 nm Cu, 0.5 to 3 nmCu/0.5 to 3 nm Ag/0.5 to 3 nm Cu, 0.5 to 3 nm Pt/0.5 to 3 nm Cu, 0.5 to3 nm Cu/0.5 to 3 nm Pt/0.5 to 3 nm Cu, 0.5 to 3 nm PtCu/0.5 to 3 nm Cu,0.5 to 3 nm Cu/0.5 to 3 nm PtCu/0.5 to 3 nm Cu, etc. All those layersgave the same good results as herein.

Regarding the materials for the other layers, the same as in Example amay be referred to. The MR-improving layer as laminated above the freelayer in this Example d is not needed to act additionally as a seedlayer. Therefore, in this, the thickness of this MR-improving layer maybe thin to have a thickness of 1 nanometer or so. However, if the layeris too thick, it will unfavorably increase shunt current, as in Examplea. Therefore, the thickness of this layer is preferably at most 5nanometers.

The MR-improving layer below the antiferromagnetic layer is to controlthe lattice spacing in the antiferromagnetic layer, thereby preventingthe interfacial mixing in the interface between the pinned magneticlayer of CoFe and the antiferromagnetic layer (the interfacial mixingwill be caused by lattice misfit between the two layers). In addition,while controlling the lattice spacing in the antiferromagnetic layer,the MR-improving layer is to improve the pinning characteristics of thepinned magnetic layer. Concretely, the MR-improving layer may be any oflaminate films or alloy films of Al—Cu, Pt—Cu, Rh—Cu, Pd—Cu, Ir—Cu,Ag—Pt, Ag—Pd, Ag—Au, Au—Pt, Au—Pd, Au—Al, Ru—Rh, Ru—Ir, Ru—Pt, Ru—Cu, orAg—Au.

As the MR-improving layer suitable to each antiferromagnetic layer,laminate films or alloy films of two elements selected from Cu, Au, Ag,Pt, Rh, Ru, Pd, Al, Ti, Zr and Hf exhibit the subbing effect. When onlythe pinned magnetic layer is targeted, the MR-improving layer aslaminated above the free layer in the bottom type spin valve filmillustrated herein could be omitted. For the MR-improving layer thatacts as the underlayer for the antiferromagnetic layer herein, thepinned film constitution may have the Synthetic antiferromagneticstructure such as that mentioned above. One example of the SyAFstructure employable herein is 5 nanometer Ta/2 nm AuCu/7 nm IrMn/3 nmCoFe/0.9 nm Ru/3 nm CoFe/3 nm Cu/1 nm CoFe/5 nm NiFe/5 nanometer Ta.

In place of the Ta protective film, any of Ti, Zr, Cr, W, Hf, Nb and thelike is employable. Those protective films gave the same good results asherein.

EXAMPLE e

In this Example e, produced was a bottom type spin valve film of 5nanometer Ta/2 nm AuCu/7 nm IrMn/2.5 nm CoFe/2.5 nm AuCu/4 nm CoFe/2 mAuCu/5 nanometer Ta, in the same manner as in Example a. In this, theAuCu layer disposed between the lower CoFe layer (pinned magnetic layer)and the upper CoFe layer (free layer) is a nonmagnetic spacer layeracting also as an MR-improving layer for magnetostriction control in thefree layer.

In bottom type spin valve films, the fcc-d(111) spacing in the freelayer as formed in the nonmagnetic spacer layer of Cu or the like isnarrow and therefore the magnetostriction in the free layer is enlarged.However, in the film of this Example e in which the free layer of CoFeis laminated on the AuCu alloy layer acting as a nonmagnetic spacerlayer and also as an MR-improving layer, the fcc-d(111) spacing in thefree layer of CoFe is controlled on a suitable level whereby themagnetostriction in the free layer could be reduced.

The spin-dependent scattering on the interface between the nonmagneticspacer layer of AuCu and the CoFe layer is attenuated in some degree, ascompared with that on the interface between AuCu and a single-layeredCu, whereby the MR ratio in the film will decrease in some degree. Thisproblem could be solved, for example, by using a laminate film of 0.8 nmCu/0.8 nm AuCu/0.8 nm Cu as the nonmagnetic spacer layer.

The nonmagnetic spacer layer acting also as an MR-improving layer iseffective not only in the bottom type spin valve film as herein but alsoin ordinary spin valve films and in dual element-type spin valve films.One example of dual element-type spin valve films incorporating such anonmagnetic spacer layer that acts also as an MR-improving layer is 5nanometer Ta/2 nm AuCu/7 nm IrMn/2.5 nm CoFe as pinned magneticlayer/2.5 nm AuCu as nonmagnetic spacer layer and also as MR-improvinglayer/3 nm CoFe as free layer/2.5 nm Cu/2.5 nm CoFe as pinned magneticlayer/7 nm IrMn/5 nanometer Ta. One example of ordinary spin valve filmsincorporating such a nonmagnetic layer that acts also as an MR-improvinglayer is 5 nanometer Ta/2 nm AuCu/4 nm CoFe/0.8 nm Cu/0.8 nm AuCu/0.8 nmCu/2.5 nm CoFe/7 nm IrMn/5 nanometer Ta.

In bottom type spin valve films and dual element-type spin valve films,where the fcc-d(111) spacing in the free layer of CoFe is wellcontrolled by the effect of the AuCu layer which is used as theunderlayer for the antiferromagnetic layer of IrMn or the like, anyordinary Cu layer or the like may be used as the nonmagnetic spacerlayer.

The following are other examples of bottom type spin valve films anddual element-type spin valve films:

-   5 nanometer Ta/1 nm Au/1 nm Cu/7 nm IrMn/2.5 nm CoFe/0.9 nm Ru/3 nm    CoFe/3 nm Cu/4 nm CoFe/5 nanometer Ta,-   5 nanometer Ta/1 nm Au/1 nm Cu/7 nm IrMn/2.5 nm CoFe/3 nm Cu/4 nm    CoFe/5 nanometer Ta,-   5 nanometer Ta/1 nm Au/1 nm Cu/7 nm IrMn/2.5 nm CoFe/0.9 nm Ru/3 nm    CoFe/3 nm Cu/2 nm CoFe/2 nm NiFe/5 nanometer Ta,-   5 nanometer Ta/1 nm Au/1 nm Cu/7 nm IrMn/2.5 nm CoFe/3 nm Cu/2 nm    CoFe/2 nm NiFe/5 nanometer Ta,-   5 nanometer Ta/1 nm Au/1 nm Cu/7 nm IrMn/3 nm CoFe/3 nm Cu/3 nm    CoFe/2 nm Cu/3 nm CoFe/7 nm IrMn/5 nanometer Ta,-   5 nanometer Ta/1 nm Au/1 nm Cu/7 nm IrMn/3 nm CoFe/3 nm Cu/1 nm    CoFe/2 nm NiFe/1 nm CoFe/3 nm Cu/3 nm CoFe/7 nm IrMn/5 nanometer Ta,-   5 nanometer Ta/1 nm Au/1 nm Cu/7 nm IrMn/2.5 nm CoFe/0.9 nm Ru/3 nm    CoFe/3 nm Cu/3 nm CoFe/3 nm CU/3 nm CoFe/0.9 nm Ru/2.5 nm CoFe/7 nm    IrMn/5 nanometer Ta,-   5 nanometer Ta/1 nm Au/1 nm Cu/7 nm IrMn/2.5 nm CoFe/0.9 nm Ru/3 nm    CoFe/3 nm Cu/1 nm CoFe/2 nm NiFe/1 nm CoFe/3 nm Cu/3 nm CoFe/0.9 nm    Ru/2.5 nm CoFe/7 nm IrMn/5 nanometer Ta.

In place of the underlayer of Au/Cu as in the above, other variouslaminate films and alloy layers such as those mentioned hereinabove arealso employable herein.

Other examples are substrate/5 nanometer Ta/7 nm IrMn/2.5 nm CoFe/0.9 nmRu/3 nm CoFe/3 nm Cu/2.5 nm CoFe/MR-improving layer/2.5 nm CoFe/3 nmCu/3 nm CoFe/0.9 nm Ru/2.5 nm CoFe/7 nm IrMn/5 nanometer Ta. In thisstructure, the moiety of CoFe/MR-improving layer/CoFe is the free layer,in which the constituent films are ferromagnetically coupled to eachother.

In these examples, the antiferromagnetic layer is of IrMn, which,however, is not imitative. In place of IrMn, other variousantiferromagnetic materials of NiMn, PtMn, PdPtMn, RhRuMn, CrMn, Nio andthe like are also usable to produce the same good results as herein.

Spin valve films in which the pinned magnetic layer is of anantiferromagnetically coupled structure of, for example,CoFe/Ru/CoFe/IrMn (in this, two CoFe layers are as laminated via Rutherebetween are antiferromagnetically coupled to each other) alsoproduce good results of the invention. In the laminate films illustratedherein, the constituent layers each having a predetermined thickness areantiferromagnetically coupled to each other.

In the laminate films, the interlayer may be the MR-improving layer ofthe invention. For example, the laminate films are 2.5 nm CoFe/1 nmAuCu/2 nm CoFe/IrMn (in which the layers are antiferromagneticallycoupled to each other), IrMn/2 nm CoFe/1 nm AuCu/2 nm CoFe (in which thelayers are antiferromagnetically coupled to each other), etc. Apart fromthose, a laminate film of 1 nm CoFe/0.5 nm AuCu/2 nm CoFe/7 nm IrMn isalso employable, in which the layers are ferromagnetically coupled toeach other. The AuCu layer as disposed between the pinned magneticlayers is to antiferromagnetically couple the both magnetic layers toeach other, while making the interface between the coupled layers havemirror-reflectivity and stabilizing the lattice constitution in IrMn,whereby the thermal stability and the MR characteristics of the spinvalve film are improved. It is desirable that the thickness of theMR-improving layer in the spin valve film of that type falls between 0.5and 2 nanometers.

EXAMPLE f

For realizing crystal structures with good thermal stability, which havefew ordinary intergranular boundaries (ordinary intergranular boundariesin spin valve films worsen thermal stability of the films) but may havesome small angle tilt boundaries and which are not of completely singlecrystals, the MR-improving layer of a laminate film or an alloy layer ofAu/Cu or the like is effective. One example of the structure isthermally-oxidized silicon substrate/5 nanometer Ta/1 nm Au/1 nm Cu/3 nmCoFe/3 nm Cu/2 nm CoFe/7 nm IrMn/5 nanometer Ta. This was analyzedthrough sectional TEM and diffractiometry. The spot size indiffractiometry was so defined that the spot diameter could cover allregion of the laminate film to be analyzed, in its thickness direction.For more detailed analysis, the spot diameter may be more reduced as inmicrodiffractiometry.

The diffractiometry of the film gave a diffraction pattern indicating asingle-crystal-like structure in the entire region of 1 μm or more, fromwhich it is understood that the film seemingly has a single-crystal-likestructure. Except for Ta forming the underlayer and the protectivelayer, all the layers constituting the film were in fcc(111)orientation. In the diffraction pattern, another spot was seen in thesite spaced from the center point by a radius, R. This indicates thedifference in the fcc(111) spacing size between IrMn and CoFe/Cu/CoFe.In the lattice images, highly ordered fcc(111) orientation wasconfirmed. Some lattice points were found discontinued in the lateraldirection. In the entire region, the diffraction pattern gave a singlespot. It is believed that the lattice discontinuity will be forsub-grain boundaries such as small angle tilt boundaries.

The single-crystal-like structure confirmed herein is favorable, sincethe film with the structure has good thermal stability for the MR ratioand the magnetic characteristics and since the structure has fewintergranular boundaries that may cause electron scattering. In thatstructure, the mean free path of electrons is long, and the peak valueof the MR ratio is increased. The technique of producing the film havingsuch a single-crystal-like structure on an amorphous substrate such asthermally-oxidized silicon or amorphous alumina is one characteristicaspect of the invention. In this Example, used was a thermally-oxidizedsilicon substrate, which, however, is not imitative. The film formationaccording to the technique of the invention may also be effected on anamorphous AlO_(x) film formed on an AlTiC substrate, or even on anyother amorphous oxide films, amorphous nitride films or diamond-likecarbon.

In the film of this Example, the underlayer for Au does not always needto be Ta. However, Au needs the subbing buffer layer of some type.Depositing Au directly on the thermally-oxidized silicon substrate doesnot give a single-crystal-like structure such as that in this Example.As other materials except Ta usable for subbing Au, mentioned are Ti, W,Zr, Mo, Hf and alloys comprising any of them. In the underlayerconstitution of Ta/Au/Cu as herein, Ta and Au form an alloy. In this,therefore, island growth of Au is prevented, and the Au grains couldeasily undergo secondary growth. In other words, the bonding forth ofthe grains to the substrate stronger than the aggregation forth thereofhas favorable influences on the film growth.

The subbing film constitution of Ta/Au/Cu is effective for promotingsingle-crystal-like growth of grains. As in this case, when the alloyingmaterials are formed into a laminate film, Au grains to be formed into afilm do not grow as they are on Cu but form single-crystal grains astheir bonding forth to the underlayer is enlarged. The underlayerstructure like herein could not be formed in a simple Ta/Cu underlayersuch as that in 5 nanometer Ta/2 nm Cu/4 nm CoFe/3 nm Cu/2 nm CoFe/7 nmIrMn/5 nanometer Ta.

As other examples of good layer constitution, mentioned are laminatefilms or alloy films of Al—Cu, Pt—Cu, Rh—Cu, Pd—Cu, Ir—Cu, Ag—Pt, Ag—Pd,Ag—Au, Au—Pt, Au—Pd and Au—Al for Co-based magnetic layers, as inExample a. The number of layers for the laminate films is not limited,so far as two or more layers constitute one laminate film. For Ni-basedmagnetic layers, mentioned are laminate films or alloy films of Au—Pt,Au—Pd, Au—Ag, Au—Al, Ag—Pt, Ag—Pd, Ru—Rh, Ru—Ir and Ru—Pt. Like forCo-based magnetic layers, the number of layers for the laminate films isnot also limited, so far as two or more layers constitutes one laminatefilm. Of the combinations of two metals, Au—Cu, Ag—Pt, Au—Pd, Au—Ag andPt—Cu have a lot of latitude in their solid solution. Laminate films ofRu—Cu and Ag—Cu not forming solid solution could also be employedherein.

Other structures of the subbing film employable herein includeTa/Cu/Au/Cu, Ta/Pt/Cu, Ta/Cu/Pt, Ta/Rh/Cu, Ta/Cu/Rh, Ta/Pd/Cu, Ta/Cu/Pd,etc. In those, the number of the layers to be on the buffer layer of Tamay be increased. In place of Ta, any of Ti, W, Zr, Mo, Hf or alloyscomprising them may also be used. It is desirable that the fcc metallayer moiety in the subbing film is not so thick if no element capableincreasing resistance is added to the film. This is for the purpose ofpreventing the MR reduction to be caused by the increase in the shuntcurrent in the spin valve films comprising it. However, if too thin, theeffect of the subbing film as a seed layer will be attenuated.Therefore, it is also desirable that the fcc metal layer moiety is nottoo thin. Concretely, it is desirable that the subbing seed layerexclusive of the subbing buffer layer of Ta or the like has a thicknessof from 2 to 5 nanometers or so. However, when an additive elementcapable of increasing resistance is added to the subbing seed layer toreduce the shunt current, the thickness of the subbing seed layer may belarger than 5 nanometers.

In place of the fcc metal laminate films capable of forming alloys suchas those mentioned above, further employable herein are alloys of thefcc-forming combinations additionally containing any additive elements.Still other examples also employable herein are fcc alloys containing Nibut not Cu, such as PtNi alloys (of which the Pt content is preferablylarger than 26 at. % for Pt-rich alloys), RhNi alloys, PdNi alloys (asbeing magnetic in almost all compositions, adding a third element tothese is preferred), IrNi alloys (of which the Ir content is preferablylarger than 12 at. % for Ir-rich alloys), etc. Also for those alloys,the buffer metal may be any of Ti, W, Zr, Mo, Hf or alloys comprisingthem, in place of Ta. Like the laminate films mentioned above, it isalso desirable that those fcc alloy films have a thickness of from 2 to5 nanometers. If their resistance is increased by some additive elementsadded thereto, their thickness may be larger than 5 nanometers.

Specific examples of the constitution discussed herein are;

-   5 nanometer Ta/1 nm Pt/1 nm Cu/2 to 8 nm CoFe/3 nm Cu/2.5 nm CoFe/7    nm IrMn/5 nanometer Ta,-   5 nanometer Ta/2 nm PtCu/2 to 8 nm CoFe/3 nm Cu/2.5 nm CoFe/7 nm    IrMn/5 nanometer Ta,-   5 nanometer Ta/1 nm Au/1 nm Cu/7 nm IrMn/3 nm CoFe/1 nm Ru/3 nm    CoFe/3 nm Cu/1 nm CoFe/5 nm NiFe/5 nanometer Ta,-   5 nanometer Ta/1 nm Au/1 nm Cu/7 nm IrMn/2.5 nm CoFe/3 nm Cu/1 nm    CoFe/5 nm NiFe/5 nanometer Ta,-   5 nanometer Ta/1 nm Au/1 nm Cu/7 nm IrMn/3 nm CoFe/1 nm Ru/3 CoFe/3    nm Cu/4 nm CoFe/5 nanometer Ta,-   5 nanometer Ta/1 nm Au/1 nm Cu/7 nm IrMn/3 nm CoFe/1 nm Ru/3 CoFe/3    nm Cu/4 nm CoFe/3 nm Cu/3 nm CoFe/1 nm Ru/3 nm CoFe/7 IrMn/5    nanometer Ta,-   5 nanometer Ta/2 nm Cu/7 nm IrMn/3 nm CoFe/1 nm Ru/3 nm CoFe/3 Cu/4    nm CoFe/3 nm Cu/3 nm CoFe/1 nm Ru/3 nm CoFe/7 nm IrMn/5 nanometer    Ta, etc.

EXAMPLE g

The MR-improving layer mentioned hereinabove is applicable even toartificial lattice sensors such as that in FIG. 49. In the illustratedcase, the number of the magnetic layers 71 of, for example,Co-containing films or Ni-containing films as combined with thenonmagnetic layers 72 is larger than the number of the layersconstituting the spin valve film. In the case, the MR-improving layers73 are disposed each adjacent to any of the uppermost magnetic layer andthe lowermost magnetic layer. For the materials constituting the layers,the same as in Example a shall apply to this case.

The first to seventh embodiments of the invention are described indetail hereinabove with reference to the Examples, which, however, arenot intended to restrict the scope of the invention.

For example, FIG. 50 to FIG. 52 are conceptual views showing still othermodifications of the invention.

Specifically, FIG. 50 shows the cross section of a spin valve devicepart as seen from its ABS (air baring surface). FIG. 51 is a perspectiveview of a spin valve device with its gap film and shield film beingremoved.

On an AlTiC substrate 10, formed are a lower shield 11 and a lower gapfilm 12. In this, the lower shield 11 may be of NiFe, a Co-basedamorphous magnetic alloy, an FeAlSi alloy or the like, and its thicknessmay fall between 0.5 and 3 μm. For NiFe and FeAlSi alloys, it isdesirable that the surface of the lower shield 11 is polished so thatits roughness height could be smaller than the thickness of theantiferromagnetically coupling interlayer of the Synthetic pinnedmagnetic layer. The lower gap film 12 may be of alumina, aluminiumnitride or the like. On the film 12, formed is a spin valve device 13.The spin valve device 13 comprises a spin valve film 14, a pair oflongitudinal bias films 15 and a pair of electrodes 16. The spin valvefilm 14 may be a bottom-type SV such as that in Example 4. Briefly, itcomprises a nonmagnetic underlayer 141 of Ta, Nb, Zr, Hf or the like(thickness; 1 to 10 nanometers), an optional second underlayer 142 ofRu, NiFeCr or the like (thickness: 0.5 to 5 nanometers), anantiferromagnetic layer 143, a Synthetic pinned layer 144 offerromagnetic layer/antiferromagnetically coupling layer/ferromagneticlayer, a nonmagnetic spacer 145, a free layer 146, a high-conductivitylayer 147, and an optional protective film 148 (thickness: 0.5 to 10nanometers). On the spin valve film 14, formed are an upper gap layer 17(of alumina, aluminium nitride or the like), an upper shield layer 18(of NiFe, a Co-based amorphous magnetic alloy, and an FeAlSi alloy orthe like, having a thickness of from 0.5 to 3 μm). Though not shown, arecording part is formed thereover. The spin valve device 13 is of aso-called abutted junction type structure device, which is produced byremoving the track edges of the spin valve film 14 followed by formingthe longitudinal bias films in the removed sites. The longitudinal biaslayers 15 may be of hard magnetic films (comprising CoPt, CoPtCr or thelike as formed on a underlayer of Cr, FeCo or the like), or of laminatesof a ferromagnetic layer 151 and an antiferromagnetic layer 152 aslaminated in that order, for which the ferromagnetic layer is hardened.For the laminates, the antiferromagnetic layer 152 may be formed first,and thereafter the ferromagnetic layer 151 is formed thereon. Forproducing steep reproduction sensitivity profiles at the track edges forthe coming narrow-track devices, it is desirable that the magneticthickness ratio of the longitudinal bias ferromagnetic layer (hardmagnetic layer, or a combination of ferromagnetic layers as magneticallycoupled to each other via an antiferromagnetic layer) to the free layer,Ms×t (longitudinal bias)/Ms×t (free) is defined to be at most 7, morepreferably at most 5. If the free layer is so thinned that its thicknessis not larger than 4.5 nanometers (therefore having a magnetic thicknessof at most 5 nanometer Tesla), the longitudinal bias ferromagnetic layershall be also thinned (to have a magnetic thickness of at most 25nanometer Tesla) so as to satisfy the condition of Ms×t (longitudinalbias)/Ms×t (free)≦5.

In general, thin hard magnetic layers could hardly have high coerciveforce. On the other hand, longitudinal bias layers of the type offerromagnetic film/antiferromagnetic film could be more firmly coupledwhen the ferromagnetic layer 151 is thinner, since the magnetic couplingbias field is enlarged. Therefore, longitudinal bias layers of the typeof ferromagnetic film 151/antiferromagnetic layer 152 are preferred.More preferably, in the longitudinal bias layers of the type offerromagnetic layer 151/antiferromagnetic layer 152, the saturationmagnetization of the ferromagnetic layer 151 is nearly comparable to orhigher than that of the free layer for the purpose of realizing completeBHN (Barkhausen noise) removal in a smallest possible longitudinal biasmagnetic field. For this, NiFe alloys may be used, but more preferredare CoFe, Co and the like having larger saturation magnetization. If theferromagnetic film 151 used has small saturation magnetization and ifthe stray magnetic field is enlarged by increasing the thickness of thefilm 151 for realizing BHN removal, such will cause reproduction outputreduction especially in narrow tracks.

In the case of FIG. 50, the spin valve film 14 is not completely etchedbut the antiferromagnetic layer 143 is left as it is to form thelongitudinal bias layers. Apart from this case, even the underlayer 141may be etched away. Forming the longitudinal layers 15 on the remainingantiferromagnetic layer 143 is advantageous in that the electricalcontact between the longitudinal bias layers and the spin valve film isgood. In an ordinary abutted junction structure where the length of theelectrode 16 is nearly the same as that of the longitudinal bias layer15, the electrode could not keep direct face contact with the spin valvefilm. In that case, therefore, the merit of the remainingantiferromagnetic film 143 is great. On the other hand, it is desirablethat the pinned magnetic layer 144 above the antiferromagnetic film iscompletely removed and the longitudinal bias layers are formed directlyon the antiferromagnetic film. The reason is because, as will bementioned hereunder, the magnetization direction of the pinned magneticlayer 144 must be perpendicular to that of the longitudinal bias layers15. If so, the magnetization of the longitudinal bias layers 15 will beunstable owing to the magnetic interaction between the pinned magneticlayer 144 and the overlying longitudinal bias layers 15. Alternatively,the etching removal may reach the high-conductivity layer 147 but notthe free layer, and the longitudinal bias layers may be formed on theremaining free layer.

For improving the crystallinity of the layers, or for attenuating themagnetic coupling force between the antiferromagnetic layer 143 and thelongitudinal bias layers 15, an extremely thin underlayer 153 (this maybe the same as the underlayer 142) may be disposed below theferromagnetic layer 151. Even though thin, a nonmagnetic layer existingbetween ferromagnetic layers will readily make the ferromagnetic layerscoupled magnetically to each other. As opposed to this, in thecombination of an antiferromagnetic layer and a ferromagnetic layer, anonmagnetic layer existing therebetween, even though thin, cancels themagnetic coupling of the antiferromagnetic layer and the ferromagneticlayer. In order to effectively apply the bias magnetic field from thelongitudinal bias layers to the free layer, the thickness of theunderlayer 153 is preferably at most 10 nanometers. For the hardmagnetic film, it is also desirable that the saturation magnetization ofthe hard magnetic film is comparable to that of the free layer. However,in general, it is difficult to prepare hard magnetic films with highsaturation magnetization of which the saturation magnetization iscomparable to that of free layers of CoFe or the like with highsaturation magnetization.

Therefore, it is desirable that a underlayer of FeCo or the like withhigh saturation magnetization, of which the saturation magnetization iscomparable to that of CoFe, is formed below the hard magnetic film tothereby keep good balance of saturation magnetization between the hardmagnetic film and the free layer, for the purpose of removing BHN in aweak longitudinal bias magnetic field. The antiferromagnetic materialsfor the antiferromagnetic film 152 may be the same as those for the spinvalve film.

However, the magnetic coupling bias direction of the antiferromagneticlayer of the spin valve film must be perpendicular to that of theantiferromagnetic film 152 of the longitudinal bias layer. (The magneticcoupling bias direction of the antiferromagnetic layer of the spin valvefilm is in the device width (height) direction, while that of theantiferromagnetic film 152 of the longitudinal bias layer is in thetrack width direction.)

For example, the two antiferromagnetic films are made to have differentblocking temperatures Tb. First, the magnetic coupling bias direction ofone antiferromagnetic film having a higher Tb is pinned through thermaltreatment, and thereafter Tb of the other antiferromagnetic film isdefined to be around a temperature at which the magnetization directionof the ferromagnetic film (this is pinned by the magnetic coupling biasof the antiferromagnetic film whose Tb has been previously defined) isstable and which is lower than the temperature for the previous thermaltreatment, whereby the magnetic coupling bias directions of the twoantiferromagnetic films could be perpendicular to each other. For themagnetic coupling bias application to the antiferromagnetic layer 152,preferably used is a film-forming method in a magnetic field (in whichis used IrMn, RhMn or the like), or a resist-curing thermal treatmentmethod at 200 to 250° C. such as that for forming a recording region (inwhich is used PtMn, PdPtMn, IrMn or the like). For the antiferromagneticlayer of the spin valve film, an antiferromagnetic film having a higherTb (e.g., IrMn, PtMn, PdPtMn, etc.) may be used. In that case, themagnetic coupling bias direction of the antiferromagnetic film 152 couldbe pinned in the track width direction according to the resist-curingthermal treatment method, without disturbing the magnetization directionof the pinned magnetic layer of the spin valve film.

For conventional spin valve films having a single-layered, pinnedmagnetic layer, the direction of the magnetic coupling bias field forpinning the magnetic layer is disordered if the temperature for thethermal treatment for magnetic coupling bias application to theantiferromagnetic film 152 is not lowered to a significant degree. Inthis respect, conventional spin valve films are poorly practicable.However, based on the properties of the Synthetic AF structure of whichthe thermal stability for pinning magnetization is greatly stabilized attemperatures not higher than the blocking temperature of the pinnedmagnetic layer in the structure, the magnetization direction of thelongitudinal bias layer could be readily perpendicular to that of thepinned magnetic layer even when the difference in the blockingtemperature between the two antiferromagnetic films is only tens ° C. orso. Where the antiferromagnetic layer 152 is of a orderedantiferromagnetic film of PtMn or PdPtMn, it is desirable that the filmcould be ordered at resist-curing temperatures (200 to 250° C.)

It is desirable that the spacing LD between the electrodes 16 isnarrower than the spacing HMD between the longitudinal bias layers forlowering the reproduction device resistance and for realizing headsresistant to ESD. LD generally defines the reproduction track, and itmay be on a level of submicrons of from 0.1 to 0.7 μm for high-densityrecording (at least 10 Gbpsi) to which the invention is directed. On theother hand, HMD may be larger than LD by approximately from 0.3 to 1 μmso as to realize steep sensitivity profiles in the track width directionwith few influences of the hard film magnetic field thereon even thoughthe track width is narrow, thereby enabling high-sensitivityreproduction. In the condition of HD (device width)>LD and also HMD>HD,the spin valve device resistance between the electrodes can be reducedand, in addition, since the free layer in the spin valve film could havea rectangular profile of which the side in the track width direction islonger, the Barkhausen noise control is easy. Concretely, it isdesirable that the device width HD is around 0.4 μm in view of the ESDresistance of the device. For the narrow track width for which theelectrode spacing is at most 0.4 μm, it is desirable that the hard filmspacing HMD is enlarged up to about 0.8 μm.

In the case of FIG. 50 where the distance between the center of the freelayer in its thickness direction and the surface of the upper shield isrepresented by gf and the distance between that center and the surfaceof the lower shield is by gp, preferred is gf<gp for attenuating thecurrent magnetic field Hcu to be applied to the free layer. This isbecause, since the free layer is nearer to the lower shield than to theupper shield, it is more influenced by the magnetic field from the lowershield than from the upper shield, and, in addition, since the centerthrough which sense current passes is shifted to the side of thenonmagnetic spacer 145, the free layer receives the magnetic field fromthe lower shield (this is generated by the lower shield as magnetized bysense current) in the direction opposite to the sense current magneticfield direction (see FIG. 50). With the sense current magnetic fieldbeing attenuated, a larger sense current may be applied to the device,whereby higher reproduction output and better BP are obtained, or thatis, the asymmetry in the vertical direction of the reproduction waveform is reduced. Concretely, gp may fall between 35 and 80 nanometersand gf may fall between 25 and 50 nanometers with gf<gp. In thatcondition, the gap insulation could be kept, and the total reproductiongap length may fall between 60 ad 130 nanometers to realize an extremelynarrow gap.

FIG. 52 is a conceptual view of one embodiment of a head which issuitable to the top-type spin valve film of FIG. 1 and FIG. 5. The caseof FIG. 52 differs from that of FIG. 50 in that, in the former, thelongitudinal bias layers 15 are formed on the lower gap film 12 afterthe spin valve film has been completely etched away. In the case of FIG.52, it is desirable that the distance, gf, between the center of thefree layer in its thickness and the surface of the lower shield issmaller than the distance, gp, between that center and the surface ofthe upper shield. This is because, since the free layer is nearer to thelower shield than to the upper shield, it is more influenced by themagnetic field from the lower shield than from the upper shield, and, inaddition, since the center through which sense current passes is shiftedto the side of the nonmagnetic spacer 145, the free layer receives themagnetic field from the lower shield (this is generated by the lowershield as magnetized by sense current) in the direction opposite to thesense current magnetic field direction. With the sense current magneticfield being attenuated, a larger sense current maybe applied to thedevice, whereby higher reproduction output and better BP are obtained,or that is, the asymmetry in the vertical direction of the reproductionwave form is reduced. Concretely, gp may fall between 35 and 80nanometers and gf may fall between 25 and 50 nanometers with gf<gp. Inthat condition, the gap insulation could be kept, and the totalreproduction gap length may fall between 60 ad 130 nanometers to realizean extremely narrow gap.

The film constitution of the magnetoresistance effect device of theinvention can be identified in various analyzing methods.

FIG. 53 is a graph of the data of nano-EDX analysis of the cross sectionof a magnetic head which incorporates the magnetoresistance effectdevice of the invention. For example, samples for cross section TEM(transmission electron microscopy) are prepared, and subjected tonano-EDX with abeam of about 1 nanometer in diameter being applied tothe cross section of each sample, whereby the materials constituting themagnetoresistance effect device and the film thicknesses can beidentified. Considering the measurement limit and the influence ofinterfacial diffusion in thermal treatment, the film constitution couldbe almost reproduced. In particular, as will be understood from FIG. 53,the interface between the free layer and the spacer Cu and the interfacebetween the free layer and the nonmagnetic high-conductivity layer of Cuare relatively sharp, and the film thicknesses are easy to identify.

Regarding the definition of the film thickness, the half-value width ofthe peak for the material of the main element constituting the film ofwhich the thickness is intended to be determined is defined as thethickness of the film. For example, the spacer Cu and the nonmagnetichigh-conductivity layer (underlayer) of Cu give a sharp peak, theirthicknesses are easy to determine. Based on these, therefore, thethickness of the free layer is defined as the region sandwiched betweenthe upper and lower Cu layers. In the example of FIG. 53, the thicknessof the spacer Cu is determined to be 2.4 nanometers, and that of thenonmagnetic high-conductivity layer to be 2 nanometers. The totalthickness of the free layer as sandwiched between the two Cu layerscould be 4.1 nanometers. The thus-calculated thickness of the free layeris to nearly reproduce the intended free layer thickness of 3.7nanometers. Through the analyses noted above, the film constitution ofthe spin valve film of the invention could be identified, and thethicknesses of the spacer layer, the nonmagnetic high-conductivity layerand the free layer (even though it is extremely thin) could be measuredrelatively accurately.

The invention can be carried out in the manner of the embodimentsmentioned hereinabove, and has the following advantages.

According to the first embodiment of the invention, provided is a spinvalve film with good bias point control, high MR and high ΔRs, which,however, could not be realized by merely thinning the free layer inconventional spin valve films. The margin for process latitude inproducing the spin valve film of the invention is broad. Thus, the spinvalve film of the invention is favorable to the coming new-generationdevices in the art.

According to the second to sixth embodiments of the invention, providedare a magnetoresistance effect device (MR device), especially a giantmagnetoresistance effect device (GMR device), in which the pinnedmagnetic layer is kept stable even at high temperatures of around 200°C., and also a magnetic head incorporating the device. With coming harddisc drives being directed higher density recording, the temperature ofthe magnetic head in operating disc drives will be often high. Themagnetic head of the invention is operable at such high temperatures. Inaddition, even when electrostatic discharge current flows into the MR orGMR device of the magnetic head, the pinned magnetization of the pinnedmagnetic layer in the device is not disturbed by it and is kept stable.In addition, since the shunt of sense current is small in the device,high resistance change is kept in the device to ensure good reproductionsensitivity. Therefore, with the magnetic head of the invention, muchhigher density recording is possible, and much higher reproductionoutput can be attained.

According to the seventh embodiment of the invention, the degradation ofMR ratio in the spin valve films in thermal treatment such as annealingcan be prevented, and, in addition, MR ratio in the device can beimproved through improved specular reflection in the layers constitutingthe spin valve film in the device. Even when the free layer in the spinvalve film in the device is thin, the interlayer between theMR-improving layer and the free layer is kept stable. Therefore, afterthermal treatment, the electron transmission through the interface iskept high, and the spin valve film can maintain high MR ratio. Moreover,the magnetostriction in the free layer of, for example, a Co-basedmagnetic material can be reduced by the MR-improving layer, and themicrocrystalline structure of the free layer can be well controlled.With these advantages, the MR device of the invention is characterizedby its high output power, few noise troubles and high thermal stability.

As has been described in detail hereinabove, the invention realizeshigh-performance and high-reliability MR devices, and its industrialadvantages are great.

While the invention has been described in detail and with reference tospecific embodiments thereof, it will be apparent to one skilled in theart that various changes and modifications can be made therein withoutdeparting from the spirit and scope thereof.

1. A magnetoresistance effect element, comprising: a nonmagnetic spacerlayer; first and second ferromagnetic layers separated by thenonmagnetic spacer layer, the first ferromagnetic layer having amagnetization direction at an angle relative to a magnetizationdirection of the second ferromagnetic layer at zero applied magneticfield, the magnetization of the first ferromagnetic layer freelyrotating in a magnetic field signal; a magnetoresistanceeffect-improving layer comprising a metal-alloy film and disposed incontact with the first ferromagnetic layer so that the firstferromagnetic layer is disposed between the nonmagnetic spacer layer andthe magnetoresistance effect-improving layer, the metal-alloy filmdisposed in contact with the first ferromagnetic layer and not forming asolid solution with a metal element of the first ferromagnetic layer,the metal-alloy film comprising first and second elements that form asolid solution with each other; and a nonmagnetic underlayer or anonmagnetic protecting layer disposed in contact with themagnetoresistance effect-improving layer so that the magnetoresistanceeffect-improving layer is disposed between the first ferromagnetic layerand the nonmagnetic underlayer or the nonmagnetic protecting layer;wherein the metal element of the first ferromagnetic layer is nickel,said first ferromagnetic layer being a Ni-alloy, wherein said firstelement of said metal alloy film is Ru and said metal alloy film has Ruas a main component.
 2. A record/reproducing magnetic head, comprising:a substrate; a lower magnetic shield layer formed on a main surface ofthe substrate; and a magnetoresistance effect element formed on thelower magnetic shield layer, wherein the magnetoresistance effectelement includes, a nonmagnetic spacer layer; first and secondferromagnetic layers separated by the nonmagnetic spacer layer, thefirst ferromagnetic layer having a magnetization direction at an anglerelative to a magnetization direction of the second ferromagnetic layerat zero applied magnetic field, the magnetization of the firstferromagnetic layer freely rotating in a magnetic field signal; amagnetoresistance effect-improving layer comprising a metal-alloy filmand disposed in contact with the first ferromagnetic layer so that thefirst ferromagnetic layer is disposed between the nonmagnetic spacerlayer and the magnetoresistance effect-improving layer, the metal-alloyfilm disposed in contact with the first ferromagnetic layer and notforming a solid solution with a metal element of the first ferromagneticlayer, the metal-alloy film comprising first and second elements thatform a solid solution with each other; and a nonmagnetic underlayer or anonmagnetic protecting layer disposed in contact with themagnetoresistance effect-improving layer so that the magnetoresistanceeffect-improving layer is disposed between the first ferromagnetic layerand the nonmagnetic underlayer or the nonmagnetic protecting layer;wherein the metal element of the first ferromagnetic layer is nickel,said first ferromagnetic layer being a Ni-alloy wherein said firstelement of said metal alloy film is Ru and said metal alloy film has Ruas a main component.
 3. A magnetic storage system, comprising: arecording/reproducing magnetic head including a substrate, a lowermagnetic shield layer formed on a main surface of the substrate, and amagnetoresistance effect element formed on the lower magnetic shieldlayer, wherein the magnetoresistance effect element includes, anonmagnetic spacer layer; first and second ferromagnetic layersseparated by the nonmagnetic spacer layer, the first ferromagnetic layerhaving a magnetization direction at an angle relative to a magnetizationdirection of the second ferromagnetic layer at zero applied magneticfield, the magnetization of the first ferromagnetic layer freelyrotating in a magnetic field signal; a magnetoresistanceeffect-improving layer comprising a metal-alloy film and disposed incontact with the first ferromagnetic layer so that the firstferromagnetic layer is disposed between the nonmagnetic spacer layer andthe magnetoresistance effect-improving layer, the metal-alloy filmdisposed in contact with the first ferromagnetic layer and not forming asolid solution with a metal element of the first ferromagnetic layer,the metal-alloy film comprising first and second elements that form asolid solution with each other; and a nonmagnetic underlayer or anonmagnetic protecting layer disposed in contact with themagnetoresistance effect-improving layer so that the magnetoresistanceeffect-improving layer is disposed between the first ferromagnetic layerand the nonmagnetic underlayer or the nonmagnetic protecting layer;wherein the metal element of the first ferromagnetic layer is nickel,said first ferromagnetic layer being a Ni-alloy wherein said firstelement of said metal alloy film is Ru and said metal alloy film has Ruas a main component.